This can mean either someone with ginger hair or a geek (or both). It is usually an insult.
Look at him... what a genger!
(etym. Wawarsingish) n. An incredibly hot woman with red/orange hair.
Man 1: "Got'DANG! Look at that woman; blinding white complexion, lightly freckled face and smoking hot."
Man 2: "Yeah, and she's got beautiful ginger hair too. A prime example of a genger if I do say so myself."