When there is at least one MILF within a 50 foot radius.
Two man-friends at a bar:

Guy 1: Dude me and Jane totally boned for like 3 hours last night! It was so amaz-

Guy 2: OMG! MILF Alert!

(Both men stare at a classic MILF sitting at a nearby table)
by raytk12 July 10, 2010
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