A crazy bitch with no job who does nothing but watch TV, bitch, and eat. She spends about 12 hours of her day in front of the TV, and the rest sleeping. She manages to con her new husband into giving her whatever she wants, and does everything she can to make living in that particular house a living hell.
Others who don't live with her think she can be a sweet person, but don't be fooled - she is nothing more than a succubus (assuming she's one of the good looking step moms). Otherwise, she's just some random crazy fat bitch your dad boinked after one too many cocktails.
Any bitch that your dad decided to live with is an example of a step mom.