a) If you've ever heard of 'Greek love' then you will easily understand bisexuality. The ancient Greek males would have sex with both sexes, some may have only had sex with women to procreate.
b) Liking both sexes in general, usually romantically and/or sexually. A mix between being gay and straight.
a) Alexander the Great was a bisexual.
b) Jim is dating Janie but he did date George before her.
Can be used instead of haha or huh, either a question or in agreement.
Probably originated mostly from Pinky from the Pinky and the Brain cartoon, since he said it nearly all the time.
Person 1: I heard that Paul was messing around last night...
Person 2: Narf...