Learner's definition of PEEK
to look at someone or something secretly especially from a hidden place
A little girl peeked around the corner of the chair at him.
She peeked [=peered] through a hole in the fence.
Close your eyes, and no peeking!
to look at something briefly
to show slightly
to be slightly visible
— usually + out
Take another peek at the cake in the oven to see if it's done.
They tried to sneak a peek at the actors getting ready behind the curtain.
We saw a sneak peek [=a brief showing] of the movie that will be released next month.