SCADA is the acronym for Supervisory Control and Data Acquisition and broadly defined is a computer system that monitors and controls a process. 

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An aspect in signalling refers to the colour of the signal lamp. Rail systems have different ways of describing their aspect meanings, but the following may help:

The SER is a room that houses the signalling equipment for the local railway. It usually has at least an interlocking and relays that interface to the signalling equipment in the field.

Signals have plates attached with a code to identify it from other signals. The codes, which have different meanings for different authorities, may include:

• whether the signal relates to an up line or down line.
• the distance of the signal from the capital city or its geographical location around a station
• if its an controlled or automatic signal
• to which particular line or type of train it applies

A signal in its most restrictive state is "on". Any other state is "off".

Mechanical signals are "pulled off" and electrical signals are "called off".

When a signal is returned to its most restrictive state it is "replaced" to its "on" state.

A signal in its most restrictive state is "on". Any other state is "off".

When a signal is returned to its most restrictive state it is "replaced" to its "on" state.

Signallers were used from the 1800s and utilised flags to communicate with train drivers and various technologies over the years to communicate with signallers in other signal boxes. 

Local signallers (controlling a small local area of train operations) are becoming rare; they work out of a signal box (sometimes called a signal cabin or interlocking tower). 

Modern signalling systems usually have centralised traffic control centres, where a small number of signallers can control an entire rail network. 

The main duty of the signaller is to maximise train movements in their designated area of operation.

See also train controller.

A generic term for the area between two running lines, irrespective of the actual dimension.

See also four foot and cess.

Sleepers may be timber, concrete or steel beams which are set into the ballast. The rails are secured to the sleepers. The sleepers maintain the gauge of the track by keeping the rails a uniform distance apart and they distribute the heavy loads placed on the rails over a larger surface area.