What is Cosplay?
Cosplay is the fusion of English words 'Costume' and 'Roleplay' and literally has the same meanings. The people who engage in Cosplay are known as Cosplayers. Kospure is the romaji of Cosplay, the way the Japanese pronounce it.
Cosplaying is a subculture originated from Japan, which involves cosplayers dressing up as characters from manga, anime, computer games, and even characters from books, movies and Visual-Kei rock bands in Japan. This hobby has expanded to other parts of Asia and even Europe and America.
Examples:

Cosplay of Sailor Jupiter from the anime/manga Sailormoon
Cosplay of GoGo Yubari from the movie Kill Bill

Cosplay of Alice from the book Alice in Wonderland
Getting the look
To dress up as their chosen characters, cosplayers must of course have the relevant costumes, make-up and props. The greatest aesthetic value of Cosplay is that cosplayers sew their own costumes, make their own props and wigs, and do their own make-up.
Make-up is not just about looking good, but is more often used for enhancing cosplaying accuracy:

Notice how pastel white this cosplayer's skin is. She probably used a type of powder to make her skin look pale to reflect the fairness of the character Chii from Chobits. Notice that she is also wearing a wig because Chii's hair is blond-white wheareas her own hair is black.

Notice the use of green contact lenses. They help her attain eyes exactly the same as those of the character Al Azif from Demon's Bane.
Cosplayers who are less artistically inclined may commission other cosplayers or tailors to make their costumes, or purchase ready-made costumes and props from stores catering to cosplay products. I do not wish to carry out any advertising for these websites, but if you do a google search for cosplay costumes or cosplay commissions, you should find relevant listings.
If cosplayers wish to cross-dress (Male cosplayers cosplay female characters and female cosplayers cosplay male characters), they may have to get additional items to such as fake boobs and bandages for binding breasts.
What do Cosplayers do?
Anime/Cosplay Conventions
In some countries where cosplaying is recognized as a significant hobby, conventions are hosted, where cosplayers gather so that these like-minded people may meet and interact. There may be competitions at these conventions to select the best costumes, and even skits where cosplayers act out scenes involving the characters they are cosplaying. Photographers attend these conventions to photograph these fascinating people.

Cosplayers on stage for a skit
Photography
Private photography sessions are sometimes arranged where cosplayers are photographed with a backdrop or theme relevant to the character they are cosplaying. This is usually done to retain memories of the cosplay. However, in Japan, top cosplayers create compilations of their cosplays and sell them. These photo compilations may tend to be slightly sexually provocative to boost sales.

Cover of cosplay compilation for sale

Cosplay of Princess Tomoyo for a Private Photoshoot. The photographer/cosplayer chose a royal and oriental setting for the backdrop.
Controversy
Cosplay Pornography
Just like how the school girl and maid costumes appeal sexually to some cosplay has its place in pornography too. This is most noticeable in Japan, where some Japanese pornography (AV) actresses don costumes in their movies and photoshoots. Some AV movie productions even create spin-offs of popular anime. However, sex and cosplay pornography should not be associated with the hobby itself.

Pornographic Parody of the Anime/manga The Melancholy of Haruhi Suzumiya featuring AV actress Kousaka Yuri
Original Characters / Lolita Subculture
There have been debates about whether Lolita fashion and original costume designs can be classified under cosplay, since it is also about costumes and dressing up. This may be because this does not really require acting and bringing out the personality of specific characters. However, one might argue that dressing up as an elegant lolita would require one to behave like a maiden from the victorian era, and dressing up as a fairy would require one to behave like a fairy too. Hence, it is difficult to reach a conclusion.

Snow Fairy costume

Lolita oufits
Emphasis on Cosplayer's Appearance
Since most characters are beautiful and thin, some people feel that good cosplaying can only be achieved by svelte and beautiful/handsome cosplayers. No doubt everybody likes a good-looking cosplayer, and a good-looking person will look more like a good-looking character. However, cosplaying really centers around the process of transformation - creating the costume, putting it together, sourcing for resources, studying and understanding the character... Cosplaying is not a fashion show. To hold such a superficial view is as good as identifying with cosplay pornography.
Conclusion
Cosplaying is a wholesome art. It is not simply about dressing up. It involves research on the characteristics, costumes and era of the character cosplayed, aesthetic abilities to replicate the character's appearance, and the capability to adopt the character's speech, pose and actions to reflect the character's persona. In my opinion, good cosplaying is comparable to theatre art!
Disclaimer: The above are based on my personal knowledge and experiences with cosplaying. It may or may not apply to the entire cosplay community in the world. If you have any comments or information to contribute, please do!


