Sexual partners are people who engage in sexual activity together. The sexual partners can be of any number, sex, gender, or sexual orientation. The sexual partners may be in a committed relationship, either on an exclusive basis or not, or engage in the sexual activity on a casual basis. They may be on intimate terms (in which case they are often referred to as "lovers") or anonymous, as in the case of sex with a stranger, a one-night stand, or a prostitute. A person can be another person's sexual partner even if the sexual activity is illegal, socially taboo, or otherwise in breach of a trust or commitment. A person may have more than one sexual partner at any one time, either as polyamory, polygamy or in contravention of convention.
The term sexual partner is usually applied to consensual sexual relations, not to those that are forced or result from duress, as in the case of rape. In those cases, one party is typically called the perpetrator, and the person against whom the sex act is imposed is called a victim, or by similar terminology.
A sexual partner may or may not have equal power during a sexual activity; such sexual "roles" (which can sometimes be determined by personality type but can also be determined by a conscious choice by the individual to "assume" a particular "role") typically fall under various dominance/submission (D/s) categories.
Generally, a sexual partner is one with whom one is engaging in a sexual activity, or one with whom one regularly engages in such activity and expects to do so again in the future.
An ex-sexual partner is a person with whom the other partner does not intend to engage in any further sexual activity; while a prospective sexual partner is one with whom the person has not previously engaged in any sexual activity, but desires.