Definition - What does Pizza Box mean?
A pizza box is the rectangular-shaped box in which a computer server is enclosed. It is a horizontally placed framework, usually with a number of similar servers along with it. The term ‘pizza box’ is used because the casing of the server closely resembles the thin size and shape of a pizza box, hence the name.
Techopedia explains Pizza Box
Pizza boxes are largely employed in data centers owing to their high computing power and stackability. These were primarily designed to be put onto shelves, often in a 19-inch typical rectangular box but sometimes the servers were larger, so the box had to be cut off in order to fit them. Since the dot com boom (late 1990s), pizza box servers have become a crucial part of web data centers and industrial applications where rack space and density is an important deciding factor in choosing the right server.