Flirting is eliciting sexual interest without serious intentions. It involves body language and is normally an innocent sexual game, playing at love.
Flirtatious behaviour can be part of someone’s normal behaviour pattern or it can be restricted to certain settings, for instance a party.
Sometimes girls and guys flirt for enjoyment only, while others flirt to attract a date or mate. Don’t automatically take it too seriously right away, for it might be just a game someone plays.
If you are looking for a date or mate flirting is an easy way to let someone know you are interested. If the other is flirting back you know the attraction is mutual and you can take the next step.

Female body language
Male body language

See also: eye contact and mirroring