A buzz is a vibrating sound, like the sound a bee makes. Your dog might get nervous in your yard when she hears the buzz of insects.
Buzz can be a noun or a verb: "My doorbell started to buzz like crazy when everyone showed up for my party." You can also talk about a buzz of activity, a low background noise, or describe the way stunt planes buzz the trees, flying very low. You might tell someone to "buzz off" if you're annoyed with them — this began in 1914 as a way to describe hanging up a telephone — or telling someone to hang up.