An ebauche is a French term meaning 'blank' or 'frame.' In our world, it refers to an unfinished movement, usually lacking the regulation parts (balance, hairspring, escape wheel, etc.)
Think of it as unfinished kit. Historically, watchmakers would buy ebauches, add their own parts, do the finishing and sell it as their own work.
By way of contrast, a movement is complete and ready to run out of the box. An ebauche is not. ETA sells both.