From "poseur." This usually refers to someone who attempts to be part of a clique punk, skater, goth, etc. - never preppy, but out of a desire to be recognized as a member of that clique rather than sincerity. Of late, however, the word has been overused; any newcomer is now generally considered a "poser," regardless of motive.
This word is especially popular in rambling, misspelled sessions on AIM.

someone who will be someone theyre not just to try to fit in and manipulate people. They pretend to be whatever is 'cool' at the moment than be themselves and who they really are. Then call other people posers to hide the fact they're one.

Posers spend most of their time wasting thier life away on myspace with the rest of the emo losers. They feel special they made friends with some other nobodies who no one even gives a shit about while the real popular people are making friends with known and important people.

Someone who dress diffrent then they act and try to fit into a group they don't belong in.

A person who calls someone a "poser" when the word that they really mean to use, but are to much of a poseur to realize, is "poseur".

everybody according to someone. in reality a poser is someone who pretends to be someone they are not. only acting a certain way because they want to be accepted. the problem is someone is going to call you a poser no matter what. the term has lost all meaning really. i once heard a jackass call marilyn manson a poser. really? who is he trying to be if not simply himself? so in short everybody is a poser apparently.

people who think they know crap about stuff but they really don't and it makes them look like idiots.

Someone that tries to follow whatever some one else that they admire does. They are fake to them selves. They are something they are not that is whay people hate them. Also because they are extremly annoying. They don't have a life besides being soemthing that is fake. My advice to posers be who you are. If you are really ghetto and trying to follow the HXC style be ghetto. Thats being true to yourself. Dont try to act emo when you really hate it inside. If you feel alone and helpless then try something that you truly enjoy. If the popular Clique in your school is prep and you try to be prep your going to be misrable inside because thats what you are not. Be true to yourself thats the key to happiness.