1.)someone who plays video games when bored...usually very good at it

2.) someone who plays video games as a hobby

The term "Gamer" by itself can apply to nearly anyone who plays video games on a regular basis or even once in a long while. However, even among gamers and the definitions on this site there is a large amount of debate about who and what gamers exactly are. The best way to define the term "gamer" is not to define it at all but accept that there are in fact many types of gamers out there and there is no blanket term that can cover them all.

Casual gamers are the people who mostly own console systems and buy mostly sports and racing games. They don't like fantasy games and only enjoy sci-fi games based on movies they may have seen. This group, unfortunatly, makes up the bulk of the gaming community and the current popularity of shitty games on shitty console systems is evidence of this. Casual Gamers think that having a "life" consists entirely of getting laid and drunk on a regular basis and have very little interest in games outside of a way to pass the time without spending alot of money.

The group of people who call themselves Hardcore gamers aren't often quite as "hardcore" about gaming as they would like to think. These are the people you see complaining that games now come in fancy modes like "3D" and debating the finer points of why Final Fantasy 6 was better than Final Fantas...

1) Someone who plays videogames for a hobby.

Somebody who finds refuge from the sheer mundanity of everyday life in the bosom of a particularly engrossing videogame. General stereotypes have already been mentioned, but in my experience with fellow gamers, they are largely misanthropic and just find most people uninteresting. This could perhaps explain why many are seen as socially inept and introverted, but then again, I doubt misanthropia is a popular mindset. The gamers I know are well-read and erudite (in contrast with the idea that games 'rot your brain' - ever noticed how people who make such claims are usually Big Brother watching idiots themselves?).

A gamer is someone (can be male or female) who plays games more than once a week (sometimes even 2 or 3 times a day). I'll just have all you haters out there know that most gamers are not socially handicapped, nerds, and usually have a hell of a lot more friends than non-gamers. Also, if any of you haters out there spent any time at all in the daylight instead of on the internet bashing gamers, maybey you would see that the gaming community is a LOT bigger than you imagined, and I bet that you will find at least one person you know is a gamer.

Somebody who enjoys regularly playing video games.

Any other stereotypical definition is useless: I play online games a lot. I am over 40, have a girlfriend, am in good physical shape and I hold down a fairly high-pressure job. I am college educated.
Some of the younger gamers that I meet online fit the nerdy stereotype but no more than the average cross-section of high-school students. There is a higher than average number of creative professionals in the game servers I go to (probably because I go to the Mac servers).
I also have LAN parties at my house - my friends come round, we drink a few beers, get a take-away, link our computers together and fight to the death. The other three are married and two have kids. Three of us have college degrees and we are all fairly high earners.
Your stereotype is way off.

Any person who plays video games for a hobby. You have your recreational gamer who plays games only once or twice a week. You have your typical gamer who plays games once every day or every other day for a couple hours. Then you have the uber-gamers who dedicate their life to playing video games, either because of an unhealthy addiction or something job related.