Definition - What does 1U Server mean?
A 1U server is a flat server that takes up one unit of space when mounted in a rackmount or pedestal server chassis. It is shaped like a pizza box and consists of a core processor, storage, memory slots, ports and interfaces.
Techopedia explains 1U Server
The 1U server form factor is mainly used in data centers and enterprise server environments where multiple 1U server units can be installed within a single server chassis. A 1U server is designed to correspond to a server's physical dimensions and how it is assembled/fit with a server chassis. The U represents number of units, meaning that 1U fills one unit of space in the server chassis. In most server chassis designs and servers used in them, 1U is equivalent to 1.7 inches high, 19 inches wide and 17.7 inches deep.