Two Young Blonde Girls Couple Taking Off Their Clothes

In social psychology a significant other is the parent, uncle/aunt, grandparent, or teacher—the person that guides and takes care of a child during primary socialization. The significant other protects, rewards, and punishes the child as a way of aiding the child's development. This usually takes about six or seven years, and after that the significant other is no longer needed, the child moves on to a general other which is not a real person, but an abstract notion of what society deems good or bad.
First use
The first known occurrence of the term was in 1953 by US psychiatrist, Harry Stack Sullivan, a former editor of the journal Psychiatry, in his posthumously published work, The Interpersonal Theory of Psychiatry. While the term currently enjoys use and familiarity, greatest use of the term peaked in the late '80s to mid '90s and has generally declined since then in favor of other terminology as deemed appropriate. However, because much of the other terminology is somewhat cumbersome, the use of the term "sigo" is beginning to gain some popularity.