The word cosplay is actually a blending of the words -costume and play. Cosplay girls are called this because not only do they dress up like their favorite characters, but they also act out skits and pose for pictures as the characters just like actors in a play.
Most cosplayers dress up for conventions, where they can participate in on-stage skits and costume contests. They mingle with other like-minded people who will often recognize their character on sight. Many web sites post galleries of pictures of cosplayers they spot at conventions, and some people even have stores where you can purchase a costume if you don't feel like making your own.
Cosplayers gather from all over the world to attend conventions. Some practice speaking like the character and stay in character during the entire convention, especially while having photos taken. Others simply enjoy wearing the same outfit as their favorite character and don?t act any different than normal.
Occasionally cosplayers will pose for gag pictures in which they are doing something the actual character would never do. An example would be an extremely violent character suddenly hugging everyone and doing the peace sign at the camera with no weapons in sight.
In fact, some cosplayers' entire costumes are parodies! They will dress up as a made-up character that is obviously parodying the outfit of an existing one. These cosplay parodies are funny to see and infinitely more amusing if you've seen the show or read the book that features the things they're making fun of.
Those who cosplay seriously often make their entire costume from scratch. This means sewing their costume-creating such items as swords and bejeweled shoulderpads. Depending on the character, they might even make prosthetic limbs! Any cat-girl cosplayer can tell you that having a well-made set of cat ears and a tail can really make the costume.
Others wear wings for angelic or demonic characters, apply makeup for characters who have unique complexions (like the indigo blue or obsidian black drows) and wear false fangs or long fingernails to emulate a character's exact look. Many wear wigs, but some determined cosplayers even grow their hair out or cut it short and color it to match their cosplay character.
Cosplay girls dress up solo or with friends and family, and sometimes they form cosplay groups. These groups all dress up as characters from one particular story, so that when they attend a convention it will look like the whole cast of the show or book is present! It's much more fun to act like a character if you have another character from the same story to act with.