There would appear to be conflicting opinion as to what makes a mono-print and a mono-type respectively and there are plenty of books on the subject. I make no distinction and call them mono-prints, each one is a unique one off print.
There are many ways to produce mono-prints. I usually use a metal or perspex plate, apply ink with brushes and rollers, then place a sheet of paper over the plate, and either run it through an etching press, or press by hand using a baren,and a hard rubber roller.
Some prints consist of several layers of ink applied and pressed as above, whilst others involve a single pressing. Either way each print is unique. The beauty of mono-prints is that whilst they are a reproduction of a painting that is done on a plate, the pressing process creates marks that would be impossible to achieve by hand. Although it is possible to do several versions of a mono-print by applying more ink to the plate no two prints are ever identical.