1. a brief glimpse or showing of something
take a sneak peek at something
This expression is common in both a social and professional context and is usually used in two different ways. Firstly, you can take a brief and furtive look at something that you particularly are not allowed to see, or that is generally supposed to be kept a secret. Secondly, you can be given a chance to see at least part of something that has not yet been made public or fully available. 'A sneak preview' has a similar meaning.