A very outgoing mother who has already slept with most of the people that Tom is associated with.. and most of the town for that matter.
Tom's mom can be put into any sloganizer to get some pretty funny results such as "It's Quick, It's Easy, It's Tom's Mom"
Tom's mom can be used as a come-back to any person named Tom, and usually is a hit with the crowd. The phrase is rapidly becoming a popular thing to say even in conversations that dont involve anyone named Tom.
Scott: Who did you take to the movies last night?
Sean: Tom's Mom