1.one who pretends to be someone whose not.
2. who tries to fit in but with exaggeration

Any one who does not follow his/her own ideas of what he/she likes. Following no one set norm makes you real and following no one set norm makes you poser. Poser is governed not by the clothes, music, or makeup you wear, but rather by the state of your mind and the conformity to your own beliefs.

A person who attempts to blend into a specific social group.

a person - usually in middle or high school, who is insecure about him/herself and trys very hard not to be a "conformist" or a "prep," by doing things like: purchasing a skateboard or guitar, purchasing a great deal of clothing and accessories from hot topic, and listening to pop-punk bands such as simple plan, yellowcard, etc. usually, this supposedly "nonconformist" behavior just backfires on him/her, because now he/she is still conforming, just to a different group of people. so the moral of the story is to be yourself.

Someone whos acts like someone theyre not,but not realizing that there being fake, basically a loser trying to fit in.

A poser is someone who tries hard to be something they arent. Usually, posers call other people posers because they are jealous that the person they called a poser is more skater/stoner/goth/punk/rocker/grunge/etc. than they will ever be.

One who attempts to appear to others as something they are not, especially by their manner of dress; a charlatan.

also 'poseur'