A fixed signal, either a controlled signal or an automatic signal, is one that has been placed in a fixed location. The location is selected to cater for the largest braking distance of the various trains that use the line. Another factor that governs a fixed signal's location is geographical features (such as tunnels, curves, declines and inclines). 

See a different type of signalling, in-cab signalling.

Flank protection is provided to prevent a route being set that crosses the path of a train route already set. Vital interlockings (relay or computer based) apply interlocking rules for setting the route by checking track occupancy plus other point and signalling status on the requested route.

A generic term for the area between the two rails of a running line, irrespective of the actual gauge dimension.

See also six foot and cess.

A railway car that carries freight and can be an open or closed arrangement.

The "V" shape formed by the merging of the two rails in a crossing.

Frogs may be fixed or movable.

A front contact of a relay is made (makes an electrical circuit) when the relay is energised.

See also back contact.

Gantries have plates attached with a code to identify it from other gantries. The codes, which have different meanings for different authorities, usually state the distance of the gantry from the capital city or its geographical location around a station.

The rail gauge is the inner distance between the heads of the two rails in a rail line.

• A broad gauge is usually 1,600 mm (5 ft 3 in).
• Most of the world's railways use a standard gauge of 1,435 mm (4 ft 8½ in).
• A narrow gauge is usually 1,067 mm (3 ft 6 in).

Where a vehicular road / pedestrian footpath and a rail line cross at the same lever (or same grade).

Grade crossings are commonly referred to as level crossings and they may be passively protected or actively protected.

Alternative to grade crossings are grade separations where bridges over or under the rail line (or tunnels) are employed. 

A greenfield is a site which lacks any constraints imposed by prior work. It is usually a new facility. 

A brownfield is a site with established constraints. It may be an operating, abandoned, idle, or under-used facility.