Letterpress explained

Letterpress makes me happy. There is something about the process that makes it seem antique and romantic, like you would find a letterpress card inside a glass bottle floating at sea. I never really understood the process until now. The art of letterpress is so unique and special is because each color and each piece of paper has to be printed on its own. The inventor of this amazing art was Johannes Gutenberg in the mid-15th century until the 19th century. It remained in wide use for books and other uses until the second half of the 20th century. In addition to the direct impression of inked movable type onto paper or another receptive surface, the term Letterpress can also refer to the direct impression of inked printmaking blocks such as photo-etched zinc "cuts" (plates), linoleum blocks, wood engravings, etc., using such a press.[wikipedia]

 Susan from SIMPLESONG press explains the process of letterpress via Design Sponge.

Illustrator is used for the design portion of the work. The artwork is then sent out for platemaking – she uses Boxcar press for this. Once the plates are received the press is prepared. The paper is trimmed and the ink is actually mixed by hand. Each item is printed one at a time.

In letterpress printing, each color requires a separate plate and an additional run through the press.