Nomo is short for "non-monogamy" or "non-monogamous." It is a term that is gaining acceptance in the alternative lifestyle community, particularly among those who reject the term "swinger" to describe their sexual practices but do not identify as polyamorists.
The ironic play on the word "normal" in "nomo" also appeals to non-monogamous couples who otherwise live in the mainstream (i.e., are married, have children, etc.).
Julie and Patrick are a nomo couple. Sarah is their girlfriend.