A kazoo is a musical instrument that you play by humming into it. The sound a kazoo makes is a silly, buzzing one. You wouldn't want to spend a relaxing evening listening to kazoo tunes.
Kazoos are small, simple toys made of metal or plastic. All you have to do to play a kazoo is hum a tune. A membrane inside the kazoo vibrates, turning your humming voice into a musical sound. Kazoos were invented in the 1880s, and in the US they were given the imitative name kazoo, from the earlier slang bazoo, or "trumpet." In the UK, kazoos were originally called "Timmy Talkers."