Real Dictionary

gap
countable noun: A gap between two groups of people, things, or sets of ideas is a big difference between them.
countable noun: A gap is a period of time when you are not busy or when you stop doing something that you normally do.
countable noun: A gap is a space between two things or a hole in the middle of something solid.
countable noun: If there is something missing from a situation that prevents it being complete or satisfactory, you can say that there is a gap.

gap in American English
a hole or opening, as in a wall or fence, made by breaking or parting; breach
to come apart; open
to make an opening in; breach
intransitive verb: to come open or apart; form or show a gap
noun: a break or opening, as in a fence, wall, or military line; breach
transitive verb: to make a gap, opening, or breach in

gap in British English
noun: a break or opening in a wall, fence, etc