In relationship/sexual terminology, this is the Stage in dating where while making out or making love, the couple advances by heavy petting and touching, while potentially removing a few articles of clothing.
This can include touching of the womans bare legs, breasts, and hips. This can lead to the touching of private-areas.
For some, this can lead to stimulating one-anothers private regions by Touch.
In more hardcore culture, this can also include oral sex or fingering. [See also Mutual Masturbation]