Tomboy

A tomboy is a girl who does things which are similar to the gender role of a boy.Tomboy in the Online Etymology Dictionary 

They might also wear masculine-type clothes and play games and take part in activities which are often quite physical. This type of thing is usually thought to be done more by boys.

The opposite of a tomboy is a femboy (a boy who does things which are similar to the gender role of a girl).

 References 

Category:Gender
Category:Pejoratives