Cosplay is the use of costumes to imitate or represent characters found in manga, anime and comic books. There are periodically conventions of young people dressed in costumes. I saw a conference in San Francisco in Japantown with over 5000 young attendees. There have been similar events in San Diego with over 100,000 attendees.
What I want to point out is that the word cosplay went from English as costume play to Japanese as cosplay and now back to English.
The Japanese very frequently use English words and phrases and modify them for their own use as they did in this case with costume play. There are many words now in the English language that underwent this morphology.
There will be many more such English to Japanese to English constructions in the future.