there are really two definitions.
1.
Catch-phrase from Douglas Adam's book "
The Hitchhiker's Guide to the Galaxy." Deceptively simple to understand, and yet this simple advice really can improve the quality of your life if you choose to follow it.
2. First song on
Coldplay's debut album, "Parachutes," and also the first song on the "Garden State" Soundtrack. A short but very nice song. When you hear the song, and then read the book it becomes that much better.