it's a jet that does not require a turbine. The germans used them in the V1 buzzbombs that they sent toward London in WW2. The type I'd build is a Lockwood pulsejet, which is a U shaped tube with no moving parts. You inject propane into it and light it off.
This site should give you plenty of info if you're curious. And bored.
http://aardvark.co.nz/pjet/lhkart.shtml
One read of that and you'll understand why I think I might just die if I try to build one
