Mind the gap

"Mind the gap" or sometimes "watch the gap" is an audible and written warning phrase issued to rail passengers to take caution while crossing the horizontal, and in some cases vertical, spatial gap between the traindoorway and the station platform edge.

The phrase was first introduced in 1968 on the London Underground in the United Kingdom. It is popularly associated with the UK among tourists because of the particularly British word choice (this meaning of the verb has largely fallen into disuse in American English, where the term "watch your step" is more commonly used).