A スケバン (sukeban) is a female delinquent character, a gang type - and generally it's leader. Recognizable with her longer-than-normal skirt, her weapon of choice - probably a bokken and - if she is great enough - a long sleeved jacket with the gang's name written at it's back or something like 'courage!, power!, victory!' - something flashy. Also greatly associated with the winter sailor dress - not the white ones, but the dark ones.
Their personality is well, that of a delinquent - airy, standing, and harsh. Getting in to trouble by first holding one feet high on some table or something, resting her weapon (which is there, no matter what) on her shoulder and shouting the brand "Oi, oi oi oi!" while doing this is common sense among them. Also the pose you see on the right is always done with the rest of the gang standing behind.