Symbiosis

[Sarah]

The living together in more or less imitative association oreven close union of two dissimilar organisms. In a broad sense theterm includes parasitism, or antagonistic, or antipathetic,symbiosis, in which the association is disadvantageous or destructiveto one of the organisms, but ordinarily it is used of cases where theassociation is advantageous, or often necessary, to one or both, andnot harmful to either. When there is bodily union (in extreme casesso close that the two form practically a single body, as in the unionof algæ and fungi to form lichens, and in the inclusion of algæ inradiolarians) it is called conjunctive symbiosis; if there is noactual union of the organisms (as in the association of ants withmyrmecophytes), disjunctive symbiosis.

[Sarah]

It's a science term for [friends with benefits]