Snoring is that rumbling sound people make when they're fast asleep. It happens when air flows past relaxed tissues in the throat, causing them to vibrate. Some folks snore lightly like a distant motorcycle, while others could rival a chainsaw chorus!
There's actually a whole spectrum of snoring sounds - from the gentle 'zzz' to what I call 'bear mode.' My roommate in college used to produce these epic snorts that'd wake the neighbors. Funny thing is, the person snoring usually sleeps right through it while everyone else gets a free (and unwanted) sound machine.