1. AOL is a company, while AIM is a software, developed and maintained by AOL.
2. AOL is short for America Online, a corporate internet service provider (ISP). AIM is the initials of AOL Instant Messenger, a cross platform instant messaging program.
AOL used to be dial up...and it cost $ monthly...remember when your mom used to say "get off AOL, I'm expecting a phone call!!" well, you probably don't unless you were born in the 80's.
AIM is a free service and always has been.
You want to learn more? -
http://justinakapaste.com/
http://www.differencebetween.net/technology/internet/difference-between-aol-and-aim/
http://en.wikipedia.org/wiki/AOL
I think I might have to put this in my signature. No offence. Damn, I'm old.