To overdo something means to do too much of it, past the point where it's helpful or good. When you overdo the salt in a recipe, the food tastes terrible. When you overdo exercise after a long break, your muscles ache for days. When a comedian overdoes a joke by repeating it endlessly, it stops being funny.

The trick is recognizing when enough is enough. A little effort improves things, but too much creates problems. You might study hard for a test (good) but overdo it by staying up all night and feeling exhausted the next day (bad). You might decorate a poster with some drawings and colors (nice) but overdo it by cramming every inch with glitter and stickers until no one can read the words (too much).

People often overdo things when they're excited or nervous. An actor might overdo their performance by gesturing wildly and shouting every line. Someone telling a story might overdo the details until listeners get bored.

The related phrase “don’t overdo it” is friendly advice to pace yourself, like when you're recovering from an illness or trying something new. Finding the right balance takes practice and attention to results.