A Reprap is an open source, 3D fabrication machine. If you are familiar with the Schlockverse, think of it as a primitive fabber. If you know about Star Trek, think of is as very (!) primitive replicator.
If you somehow are not familiar with ether of those references, I will describe a Reprap for you. In essence, a Reprap is a personal, printer sized machine capable of "printing" plastic objects.
They can make everything from the practical to the complicated to the whimsical. (Images from Thingiverse.com)