A limit is a boundary, or how far something can go, or the maximum amount of something. When you reach the limit, imagine a little sign saying "the end."
There's a limit to how much weight you can lift, how many words can be written in an hour, or how long someone can stay awake. Once you pass the city limits, you have left town. Sporting events have time limits. As a verb, you can limit how much chocolate your kids are allowed to eat. And if you don't feel like writing much, you'll limit your essay to just 400 words instead of 500.