Bossa nova started in Rio de Janeiro in the late 1950s. Musicians began playing samba in a quieter, smoother way - with the same beats hidden under soft chords and whispered singing. It sounded so different from anything else that they called it 'a new wave'. Within a few years, people all over the world were listening to it.
The most famous bossa nova song is 'The Girl from Ipanema', written by a Brazilian called Antônio Carlos Jobim. It has been recorded and sung by musicians in dozens of languages around the world, and is one of the most-recorded songs in history.
Bossa nova is often played on a nylon-string guitar. The player picks the strings gently with their fingers (rather than strumming) to make a soft, rolling sound. A singer comes in quietly on top, almost like they're talking to themselves.
If samba is the music of a Brazilian street party, bossa nova is the music of a Brazilian sofa, a beach in the late afternoon, or a quiet café. They are like cousins: same family, very different mood.