Meaning intellectual, or very bright.
Also, may be the stage of inercourse when the male may become aroused, or sexually ready for intercourse. When semen flows to the penis. When the penis becomes excited and gets hard and "stands up", for the sexual pleasure of a female, or another male.
Felmale: "Hunny, did you Derrick yet?"
Male: "Wait, I just got it, let's go!"