A shortening of 'Significant Other;' particularly useful when addressing a mixed gender group with varied marital statuses. Frequently pluralized: sig o's.

Noun: a friend who is usually only called upon by a friend when a more primary/prominent friend is unavailable.

Taken from the term “second string” in an athletic competition situation. In football, if the star quarterback gets injured during a play, the second string is called off the bench to replace him/her. A “Second String Friend” is essentially benched until needed, if ever.

Synonyms: Plan B, Second Choice, Secondary Friend, Benched Until Needed

Abbreviation for "significant other". Used by couples uncomfortable with the immature and trivial connotation of "boyfriend" and "girlfriend", the homosexual and/or business inference promoted by "partner", and the formality of the lengthy "significant other". Primarily used by couples over 30.

-noun (sig -o)
1. Shortened version of 'Signal Officer', primarily in the Army. Most often used to refer to the latter instead of his/her name and rank.
2. Can be used to refer to the Signal Officer at any level of command (e.g. Battalion Sigo, Brigade Sigo, Division Sigo).

SigO is simply a sane, efficient way to say one of the most frequently used terms in Western Culture, Significant Other, without babbling out six (6) syllables.