S.
Saddle Tank : A steam locomotive which carries its water in tanks draped over the boiler barrel like a saddle.
Sand drag : A short length of railway track buried in sand, and running from a set of catch points. It is designed to bring runaway vehicles to a halt rather than derailing them.
Scale : The size of things on a model railroad relative to things on a real railroad. For example, in the most popular scale, HO, models are 1/87th full size.
Scatter materials : These are purchased or ready made ground up materials which are scattered on a sticky surface to represent grass, earth or foliage. Made from sawdust or different kinds of foam usually. Available in many colours and grades from various manufacturers.
Scenic break : A way of dividing up a model railway to make it look as if two or more sections are further apart than is the fact.. This effect can be achieved by making your train disappear through a cutting, or under a bridge. A tunnel, as in my own case, can be used and the exit is hidden by scenery so that it can be as far away as you want it to be, many miles or hours away if needs be.
Scissors Crossover : Two crossovers interlaced with a crossing in the middle which allow trains to pass from one parallel track to the other in either direction.
Scratch-built : The model is built from parts that you have made, or mostly made, yourself.
Scratchbuilding : Making a model from raw materials and parts, not using kits.
Scribing : This is a method of marking out planking, brick or stonework etc on the material of your choice by using a pointed instrument or blade to indent or cut into the material so as to give the effect of relief. When colour is applied to the whole the cuts or indentations stand out.
Sectional Track : Track in short, rigid pieces (fixed length and curve radii) that are easily joined to each other.
Semaphore Signal : A signal where the indication is given by a movable arm or board.
Setting Down Post : A lineside post upon which, without needing to stop, a member of a train crew places a single-line staff.   
Shay : A type of geared steam locomotive used extensively in logging, mining, and industrial railroading. It had three cylinders mounted vertically on the right side of the boiler driving a crankshaft geared to all the axles.
Shed Pilot : A locomotive used within the bounds of a locomotive depot for moving disabled locomotives, or locomotives out of steam.
Short Section : A block section which is so short that distant signals, which would normally be located inside the block section, are mounted on the same posts as the starting signals of the block posts in rear.
Shoulder : The raised edge of the ballast.
Shunt : To move or rearrange rolling stock within the bounds of a station or goods yard.
Shunt Ahead Signal : A Shunt-ahead signal authorises a move past a Section Signal for the purpose of then setting back (e.g. into a siding).
Shunter : A locomotive used for shunting.
Shunter's Pole :  A pole with a hook on it, used by a shunter (person), for unhooking loose couplings.
Shunting Neck : The length of track joining a reception road in a marshaling yard to the sorting sidings.
Side Tank : A steam locomotive which carries its water supply in tanks mounted on the running plates on either side of the boiler.
Siding : A length of railway track used for storing rolling stock between journeys.
Siding Signal : An auxiliary signal which controls the exit from a siding on to a running line. When of the semaphore type, these signals often have a large circle fixed to the arm.
Signal : A device used to indicate to a train driver whether he must stop; whether he may proceed normally; or whether he must proceed with caution.
Signal Check : An unscheduled stopping or slowing of a train due to adverse signals.
Signal Gantry : A framework suspended across several train tracks, and upon which many signals may be mounted.
Signal Section : The length of running line between any two consecutive stop signals.  
Simulator : This is sometimes called "inertia" or "momentum". It allows controllers so fitted to automatically accelerate a train, allow it to coast or be braked to a standstill. This is achieved by two controls, a regulator and a brake and gives more realistic acceleration and braking. In Gaugemaster controllers it can be switched off to allow the controller to be operated with standard control.
Single Slip : A special condensed track component that combines the functions of two turnouts in a short distance. Allows only three possible routings, not the four of a double-slip.
Single Track : A railway route where only one track is provided for both directions of travel.
Sleeper : A beam spanning the track which is used to support the rails. Originally wooden but concrete sleepers are generally used now. Steel sleepers have also been used occasionally.
Sleeping Car : A railway coach in which beds are provided for passengers to sleep in.
Slip : A diamond crossing interlaced with two or four sets of points (see single slip and double slip).
Slip Coach : A railway coach which can be uncoupled from the back of a moving train, and then coast under the control of a guard to stop at the next station.
Slotted Signal : Semaphore signals which are interlocked by means of slots in such a way that conflicting indications cannot be given. The system is most commonly used at the entrance to a short section, where the distant arm may not be pulled off unless the corresponding starting signal, on the same post, is first pulled off.  
Solenoid : A coil of wire wound around a hollow core which creates a magnetic field within the core when electricity is passed through it.
Somerset & Dorset Joint Railway : Formed by the 1862 merger of the Somerset Central and Dorset Central Railways, this 66 mile line ran from Burnham-on-Sea to Wimborne. An important, and heavily graded, 26 mile extension from Evercreech to bath opened in 1874. In 1875 the line was leased jointly to the Midland and the London and South Western Railways.
After the 1923 grouping the line remained a joint concern between the London, Midland and Scottish and the Southern Railways. The line was closed in 1966.
Southern Railway (SR) : Formed from a number of smaller companies as a result of the 1921 Railway Act.
Splitting Signals : Two or more signals on the same post all concerned with the same approaching line, but each indicating a different route to which the line ahead may be set. As a rule, with semaphore signals, the signal for the deviating route is bracketed off the main post in the direction of the deviating route, and the height of the signal arms is arranged in respective order of the highest speed restriction of the routes concerned.  
Sprue - Stretched : A good idea for using what would otherwise be a waste product. The technique does however involve high heat and is NOT SUITABLE FOR CHILDREN. Click on this link to take you to the page where the explanation is then scroll down.
SPDT Switch : Single pole double throw. A single-pole changeover switch. Used to switch feed wires from one circuit to the next, as in Cab Control. May have a centre off position.
SPST Switch : Single pole single throw. A single pole on-off switch that either makes or breaks a circuit.
Spur : A short railway line which branches off from a main line to give access to an industry or some minor concern.  
S-Scale : Modelling to a scale of 3/16":1 foot. This scale is supported by the S Scale Model Railway Society.
Staff : An object which is the token of authority to drive a train over one section of a single line. The staff is carried in the driver's cab and therefore reduces the chance of two trains being dispatched in opposite directions along the same line.
Staff & Ticket : A system of operation on single lines when two or more trains are following each other over a single-line section without balancing workings in the other direction. The driver of one train is shown the staff and then given a ticket of authority to proceed without the staff. The last train in the procession then carries the staff.
Standard Gauge : The UK standard gauge is 4 foot 8½ inches. Anything wider is referred to as broad gauge, and anything narrower as narrow gauge.
Starting Signal : In the normal direction of travel on any one line, the last signal encountered within a block post, is a starting signal.
Station Limits : From a signaling point of view, the station limits of any block post or station area, is the length of line bounded by the most outer home-signal and the most advanced starting-signal.
Station Pilot : A locomotive which is standing-by at a station, and which may be used for any odd shunting job or emergency.
Station Throat : When approaching a station incorporating many diverging tracks, the location of the first diverging track is said to be the "station throat".
Stock Rails : The two outside running rails in a set of points.
Stop Signal : A running signal which, when in the on position, indicates that a train must stop short of the signal (see also distant signal).
Strapping : Metal strips which are used to connect together the planks of wooden- bodied wagons and vans.
Stub Points : Points which have their blades hinged at their leading ends, and in which the stock rails end where the trailing end of the points blades are met. In stub points, the blades have no shaping and they end in a stub (hence the name).
Styrene : Short for polystyrene, a versatile plastic commonly used for modeling. Comes in sheets, blocks, and rods of many different thicknesses and sizes.
Subsidiary Signal : A signal which refers to movements within station limits only, or running signals which under special circumstances override the indication of the main running signals.  
Superelevation : Raising the outside rail of curved track to help trains negotiate curves more easily and at higher speeds.
Swing Nose Crossing : A set of points incorporating a moving blade in the Common Crossing that is moved according to the lie of the points. This eliminates the `gap' in the running rails and makes for a smoother ride and reduces wear.