To teem means to be full of things, especially moving things, in such large numbers that they seem to overflow. When a pond teems with tadpoles, you see them everywhere you look, wriggling and darting through the water. When a forest teems with life, you hear birds calling from every branch, spot squirrels racing up trees, and notice insects buzzing past your face.

The word suggests abundance and movement. A library might be crowded, but an amusement park on a hot summer day teems with excited children running between rides. A coral reef teems with colorful fish swimming in every direction. Your imagination might teem with ideas when you're inspired to write a story.

Teeming describes something overflowing with activity and energy. You might read about city streets teeming with people during a festival, or a garden teeming with bees during spring. The word captures that sense of almost overwhelming fullness, like when your brain is teeming with thoughts after an exciting day. When something teems, it's bursting with so much life or activity that it can barely contain it all.