To vigorously finger a woman's vagina. Possibley using one/more/all fingers.
Bob: goddamn your hand stinks
Jeff: yea I was hand jamming your mothers rotten vagina last night.
The stroking of ones genitals using your hands; masturbating; flogging the dolphin; choking the chicken; jaggin off; sweeping the chimmney;
Hey man, what did you do last night? Oh, not too much.. Just stayed up all night hand jamming...