Blueprint is a term stemming from old-school plan-sets for buildings. The paper was blue with white lines on it (I will node more about the printing process if I learn about it).
Used more recently are "blue-lines," called so because they consist of white paper with . . . blue lines. These are printed using a large, smelly machine involving amonia somewhere (again, I'll node it if I learn it).
What I use in my work making copies and such is a large-format Xerox copier. It's a Xerox 8830 laser printer using toner; basically a normal laser printer, but made to print 36"x400' rolls of paper. There's a second unit that can actually operate as a standalone scanner. It scans the image of the blueprint being copied, and either stores it for retrieval on a desktop computer connected to the network, or it sends the image to the printer to reproduce.
Needless to say, this is a much faster and easier process than making blue-line prints. Regardless of these differences, all three formats are commonly referred to as blueprints. What is actually meant is a plan-set, which is a packet of paper with instructions on constructing a building. Often consisting of architectural sheets, mechanical systems, plumbing, electrical plans and structural designs. (See also: shop drawing)