It was the first process where CMOS was common (as opposed to NMOS).
The 1 μm process refers to the minimum size that could be reliably produced.
The smallest transistors and other circuit elements on a chip made with this process were around 1 micrometers wide.
The earliest MOSFET with a 1 μm NMOS channel length was fabricated by a research team led by Robert H. Dennard, Hwa-Nien Yu and F.H.
Gaensslen at the IBM T.J. Watson Research Center in 1974.