According to Wikipedia:

A tomboy is a girl who exhibits characteristics or behaviors considered typical of a boy,  including wearing masculine clothing and engaging in games and activities that are physical in nature and are considered in many cultures to be “unfeminine” or the domain of boys.

Just because there is a wikipedia entry, doesn’t mean we have to subscribe to it.

Some girls climb trees.

Some girls wear dresses.

Some girls climb trees while wearing dresses....