Significant other (abbreviated sig ot or SO) is a gender-neutral term to refer to a person's partner in an intimate relationship without disclosing or presuming anything about his or her marital status or sexual orientation. It is also vague enough to avoid offence from using a term that an individual might consider inappropriate (e.g. lover when he or she considers him a boyfriend, or girlfriend when he or she considers her a life partner). Nonetheless, some are offended by the implication that persons with whom one is not having a "primary" sexual relationship are "insignificant" or would as a matter of course get lesser consideration and emotional disrespect compared to the "significant" one.
The first known occurrence of the term was in 1953 by U.S. psychiatrist, Harry Stack Sullivan, a former editor of the journal Psychiatry, in his posthumously published work, The Interpersonal Theory of Psychiatry.
Its usage in both psychology and sociology is very different from its colloquial use. In psychology, a significant other is any person who has great importance to an individual's life or well-being. In sociology, it describes any person or persons with a strong influence on an individual's self-evaluation, which are important to this individual, as well as reception of particular social norms. This usage is synonymous with the term "relevant other" and can also be found in plural form - "significant others".
In social psychology a significant other is the parent, uncle, 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.