In computing, especially assembly language, a halt or stop command is a directive to cease the execution of a task. Some form of intervention is then required to start a process. In Unixhalt is the command to shut down the computer. In x86 assembly language, HLT is an instruction that halts the CPU until the next external interrupt is fired. The halting problem in computability theory is the task to decide whether a given program finishes running or will run forever for a given finite input.
In rail transport, a halt is a small station, usually unstaffed, with few facilities and normally is a request stop. In the United Kingdom most, if still in existence, have had the word halt removed from their title in recent years. Where the description is still used (verbally, if not actually on the station signs) it is usually a station served by public services but not available for use by the general public, being accessible only by persons travelling to/from an associated factory (e.g. IBM Halt), military base (e.g. Lympstone Commando) or railway yard.