What is gay partialism sex?

A sexual arousal to non sexual body parts.

Definition

A sexual arousal to non sexual body parts, such as the foot, to a greater degree than the stimulation provided by recognized sexual body parts.

Categorized in the DSM-IV, basically it is the sexual arousal, to other body parts, in an equal or greater sense, than normal organs like the penis.

An attraction to another's feet, is a popular fetish, that would be considered one showing Partialism.