the wiki sums it up best:
http://en.wikipedia.org/wiki/Barebone_computer
Most "barebones" PCs, in my experience, are unassembled parts that you need to assemble yourself. If you want assistance with picking parts for a PC, I can help you out. If you need help assembling the computer, let me know. I could either build one for you, or I could help you along the way, depending on how confident you are in your ability to put the pieces together.