Female denotes an animal which produces egg cells in order to reproduce. The female is one half of a heterogamous reproduction system, where the male is the other half. In many cases, a female cannot reproduce without sexual intercourse with a male, although some exceptions exist. What actually differentiates a female from a male is not always apparent, and in some cases more a question of definition than anything else.
'Female' and 'male' designate reproductive structures in plants, so the concept is not just limited to animals.