Mum is a casual, affectionate word for mother, used mainly in British English. When British children talk about their mum, they mean the same person American children call their mom. You'll hear this word often in British books, movies, and TV shows. A character might say “My mum's picking me up after school” or “Mum made my favorite dinner tonight.”

The word can also mean silent or quiet, as in the phrase keeping mum. When you keep mum about something, you choose not to talk about it. Maybe your friend tells you a secret and asks you to keep mum, or you discover a surprise birthday party and need to stay mum so you don't spoil it. The expression mum's the word means the same thing: keep this information to yourself.

Additionally, mum is short for chrysanthemum, a type of flowering plant with clusters of colorful petals. People often plant mums in their gardens in fall because they bloom beautifully in shades of yellow, orange, red, and purple when many other flowers have finished blooming.