A life partner is a romantic or otherwise very close friend for life. The partners can be of the same or opposite sexes, married or unmarried, and celibate, monogamous or polyamorous.
In the United States, unmarried life partners who cohabit often lack the legal rights of married couples. Nevertheless, they can enter into legal agreements, such as cohabitation agreements, deeds, and wills, with regard to their relationship and the property rights of each partner.
Same-sex life partners who are not homosexual are a common theme in serious and popular literature. Fictional examples of extremely close same-sex friends or partners who spend considerable time together on and off the job include Sherlock Holmes and Dr. Watson, Batman and Robin, Abbott and Costello, Bert and Ernie, Harpo and Chico Marx, George Costanza and Jerry Seinfeld, Jay and Silent Bob and Captain Kirk and Spock.