Top definition
When a male is faced with the question of the average rating (out of 10) of as many females he can see at a certain location or a given time.

The index is calculated = number of females / total score
GM: What's the bird index like down there?

Matt: Ow, its a solid 7.

(meaning the average rating out of 10 of all available females seen at one time is 7)
by gmach February 13, 2012
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