Pokertracker - aggression factor

[john_all_in]

Hi all first post, been hanging around the site for a good while now thought id actually sign up.

Anyway im a bit of a newbie when it comes to pokertracker, my question is this. What is classed as a very aggressive "Flop AF", "Turn AF","River AF" and "Total AF". I see people with 0.5 2.5 etc etc but dont really understand what this means. Your help would be appreciated. Cheers