Thereabouts means approximately or roughly in that amount, time, or place. When you say something happened at 3 o'clock or thereabouts, you mean it was close to 3:00, maybe 2:55 or 3:10, but you don't remember exactly. If a book costs $15 or thereabouts, it might actually be $14.50 or $16, somewhere in that range.

The word is useful when you need to give someone a general idea without claiming to be perfectly precise. A historian might say a famous battle occurred in 1863 or thereabouts if the exact year isn't completely certain. A friend might tell you to meet at the park entrance or thereabouts, meaning near that spot even if not at the exact location.

Notice that thereabouts works for numbers, times, and places. It's a way of showing that you're not completely sure, instead of pretending you know something exactly when you don't. Using it shows you're giving your best estimate while acknowledging you might be a little off.