Anyway, for me, a Gamer is a person who spends a decent chunk of their time gaming. They do not need to play everything that has ever existed, they do not need to own multiple systems, they do not need to know about everything happening in the gaming world, they just need to play games. Gaming doesn't even have to be their main source of entertainment.
With that said, anyone can call themselves a gamer. If you force a line to be drawn, where does this line go? My examples in life: I have 80-year old grandmother who plays Angry Birds, my mother who plays Dance Central 3 when I bring my 360 over, my step-brother who only plays FIFA, my Dad who plays only Mass Effect/Dragon Age, and my brother who has a PC and plays Modern Warfare 2 & Skyrim on it. Not one of these people in my life would call themselves a "Gamer" (actually, my brother might) but if they did, I see no problem with it. A gamer is someone who plays games...the end. Is that enough or do they have to be like me to qualify for "gamer" (I own a 360 and a PS3; I subscribe to multiple gaming magazines; I have a giant E-Penis Gamerscore; most of my free time is spent gaming; etc. etc.)
I have no problem with the "Casual" label if that makes a "Hardcore" gamer feel better about their hobby (I'll use the term to differentiate the crowds I'm talking about here on The Escapist but without the venom that so many seem to add); it seems silly to me to split the gaming community this way but hey, who am I to question "xX133txGm3rXx"?