The phrase "to partner" has several meanings, depending on the context in which it is used. Generally speaking, to "partner" means to join with another person or organization in a cooperative effort, or to become associated with someone or something in an activity or enterprise. In this sense, the term can be used to describe any type of collaboration between two or more individuals or groups.
For example, two businesses may "partner" by forming a strategic alliance to share resources and expertise, or two people may "partner" in a romantic relationship. The phrase is also commonly used in the context of sports, where teams "partner" with each other for tournaments or competitions.
In some cases, "to partner" can also mean to become sexually involved with someone, although this usage is less common and may be considered vulgar or informal.