What does a wrinkle in time mean?

This is in response to the answer the previous person gave. A "tesseract" is actually not something that was "made up by the author". A tesseract is actually a geometrical shape (much like a cube, pyramid, etc.) albeit slightly more complicated. It can be said to be a theoretical shape, but it's definitely not invented by the author.

As for what "a wrinkle in time" refers to in context of the book, it has been decades since I have read it so I regret I don't readily recall what the author was trying to say with that. But if you type this question into Google, you should have your answer rather quickly. Best!