S.O. is the abbreviation for significant other which could mean a spouse, life partner, or someone in a long-term, committed relationship.
In some circles, especially those discussing pansexuality or open relationships, you may come across the abbreviation O.S.O., which refers to "other significant other." Another term used is S.S.O. for "secondary significant other," used in partnerships where there are primary and secondary relationships. Related abbreviations include D.H. for darling husband, D.S. for darling son, and D.D. for darling daughter.
History of the Term
The abbreviated term "S.O." comes from online chat rooms during the early 1990s. People had to shorten long words when typing messages to reduce their time online. At the time, most internet connections were made via landline, and the time spent and the amount of information shared was limited and/or paid for by the amount of data.
Significant Other in Social and Business Uses
In many social or business situations, the term "significant other" refers to someone that offers support to another person as a friend, family member, partner, or spouse. S.O. does not refer to gender or specifically romantic entanglements, and does not specify the nature of the relationship. For instance, many hospitals now use "significant other" in their paperwork to refer to a person who can offer support during testing, treatment, or illness. Many companies will use the term on their invitations or announcements to share that the people attending the event can bring a plus one.
In the dating world, a significant other refers to a partner, girlfriend, boyfriend, spouse, or someone with whom you share an intimate, romantic relationship. Because the term doesn't imply gender, sexuality, or relationship status, many couples adopted the phrase during the 80s and 90s to avoid offense or confusion.
Synonyms for significant other include better half, civil union, boyfriend, girlfriend, domestic partner, lover, mate, partner, and spouse.
Scientific Uses of the Term Significant Other
In psychological terms, a significant other refers to someone who holds great importance to another and affects their well-being either positively or negatively. In sociology, a significant other refers instead to a person that affects one's sense of self in an important way. In social psychology, a significant other refers to someone that helps a child socialize and takes care of them during their formative years, such as a parent, grandparent, or instructor.