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A nickname for the expressway (I-285) that circles the city of Atlanta. It is one of the main highways people use to get around metro Atlanta.

The abbreviations ITP and OTP are used to define whether someone lives Inside the Perimeter (inside/close to the city of Atlanta), or Outside the Perimeter (in an outlying suburban area).
I live outside the Perimeter. There's no way I'm getting stuck in traffic for hours just to pick you up!
by ANFjon20 May 02, 2008