The answer is quite simple.
Cosplay is a portmanteau word composed of the English words costume
and playing
, a Japanese sub-culture, and a practice consisting of playing the role ones characters (manga, Japanese animation, tokuzatsu, films or video games heroes), or even ones favorite music artists, in particular by imitating their costume and makeup (usually singers of Visual kei).
Very common in Japan, this practice is not rare in the United States or in Europe during conventions and other manga or science-fiction festivals. This practice was born in the United States, originally created by fans of Star Trek then Star Wars who disguised themselves in characters for film releases, but knew a rapid growth in Japan, the country that now organizes the World Cosplay Summit.
In conclusion Cosplay is a practice very appreciated in the japanimation world. It brings joy to cosplayers as well as to the publicum.