When a person sits in the back of spanish class (or anywhere) and plays a version of the game, fire truck. In this particular version, a person slowly moves their clammy, hairy hand up another persons leg until the other person says a chosen safe word, or red light. Next, you switch roles. You try to see who can get further up the other persons leg before they say the stop word. You earn the nickname Greenlight when you let the other person go "all the way" or until the point where you engage in a fingering motion or hand job.
Everyone calls Cindy Greenlight because of what happened last week in spanish class. I can't believe she let Juan go all the way!
Through active or passive approval, a partner indicates that further advances toward anal intercourse will not be met with resistance. Active greenlight may come in the form of a verbal agreement that anal sex will ensue such as a vocalized "yes" or, in the case that the receiving party is mute, a nodding of the head. Passive greenlight is more commonly observed and relies of the absence of resistance to anal overtures rather than affirmative verbal confirmation.
After successfully placingtwo fingers in her anus, Robert knew he had the anal greenlight when Lacey did not protest.