Umpteen means a large but indefinite number of something. When your dad says he's told you umpteen times to clean your room, he means he's told you many, many times but has lost count of exactly how many. When a student complains about having umpteen math problems for homework, she's emphasizing that there are so many problems it feels overwhelming, even if she hasn't counted them all.

The word captures that feeling when something has happened so often that keeping track doesn't even matter anymore. A teacher might say, “I've answered this question umpteen times today,” meaning the exact number is less important than the fact that it's been asked repeatedly. You might hear someone say they've read a favorite book umpteen times, meaning they've lost count but it's definitely a lot.

Umpteen adds a touch of exasperation or humor to what you're saying. It's more colorful than just saying “many” or “a lot,” and it hints that whatever you're talking about has gone on long enough that you've stopped bothering to count.