As you probably know, the phrase freak dancing
is used as an unoffensive way to say "fuck dancing" but means the same thing. The girl grinds her genitals, in time to the music, gently against the boy's clothed genitals, with the aim of producing a climax of either or both dance partners. Girls have been wearing mini-skirts without panties in order to make this dance movement even more enjoyable for themselves.
Dipping is a further development of freak dancing. The girl unzips the boy to enable a dip, usually one brief shallow penetration in time to the music.
It is not considered sex, which is far more prolonged. It is more like giving each other a brief "kiss" with the genitals. If a boy tries to prolong a dip, he is avoided for at least the rest of the evening by all the girls at the dance.
I've been freak dancing for months, and I finally decided to give dipping a try too!