a small hole that lets liquid or gas flow into or out of something:
There is a leak in the ceiling.
The boat had sprung a leak (=a hole had appeared in it).
an escape of gas or liquid through a hole in something:
A gas leak caused the explosion.
a situation in which secret information is deliberately given to a newspaper, television company etc:
It became evident from the leaks that something important was going on.
to get rid of waste liquid from your body [= urinate]