Expansion of the word UNIX?

First, there was UNICS for Uniplexed Information Computing System. Then the name changed for UNIX. Same pronunciation.

Despite often being written in all caps, UNIX is not an acronym, therefore it doesn't have a full expansion. The name is a play on Multics which was an acronym (Multiplexed Information and Computing Service). That was an other early operating system around at the time of Unix creation.

Edit: As Marc stated it was originaly called Unics but once it could support multiple users it was renamed Unix which is not an acronym.

• Unix, originally Unics.
• Peter Gabriel Neumann named it UNICS (UNiplexed Infomation and Computing Service) as a pun on the multi-user MULTICS(MULTiplexed Information and Computing Service) system.
• Peter Gabriel Neumann (born 1932) is a computer-science researcher who worked on the Multics operating system in the 1960s.
• Multics was a mainframe time-sharing operating system that was developed in the 1963-1969 period through the collaboration of the Massachusetts Institute of Technology (MIT), General Electric (GE), and Bell Labs.