Crossplay is cosplay in which the person dresses up as a character of the opposite gender. Crossplay's origins lie in the anime convention circuit, though, like cosplay, it has not remained exclusive to the genre. As the name implies, crossplay is a portmanteau of crossdressing and cosplay.
In most countries that play host to hobbyists who would call themselves cosplayers, female-to-male crossplayers (females costumed as male characters, sometimes abbreviated "FtM") are far more common, due to a variety of social and cultural factors.
Many (or even most) females will crossplay for the same reasons that they would cosplay - because they like the character and/or the costume, and wish to represent that.
In Japan, female costumers tend to dominate (in numbers) the field of cosplay in general, often portraying a huge assortment of colorful characters regardless of gender.
In some countries, FtM crossplayers do not catch the public eye as any stranger than their non-crossplay counterparts. However, in yet other countries, there is a social stigma attached to FtM crossplay: some, particularly those outside the cosplay community, suspect FtM crossplayers as having penis envy, being transgendered, or having a lesbian sexual orientation. On the other hand, within the cosplay community, there is very little stigma attached to FtM.
In contrast to some of these social stigmas, most females who crossplay are not actually homosexual or transgendered and simply enjoy the art of dressing up as their favorite character. For these crossplayers, it is no different from an actress playing a male role.
Originally, in America, the most popular anime series for MtF crossplayers was Sailor Moon. Due largely to the nature of most costumes from the series (skintight tops and impossibly short skirts), this led to a negative stereotype which still exists both inside and outside of the anime community: that of the overweight, hairy-legged Sailor Soldier. This extremely derogatory stereotype has been frequently parodied, sometimes through intentionally ironic genderplay crossplay. "Sailor Bubba" and Man-Faye are primary examples of this.
In recent years, however, anime conventions have seen an increase in the number of Male to Female crossplayers who put a formidable amount of preparation and effort into the ruse of a female persona. Some males, particularly teenagers, frequently manage to recreate a striking image of femininity that can fool most unsuspecting bystanders.
Male to Female crossplay is typically divided quite definitively into these two groups: those engaging in genderplay, and those attempting to pass as female. The stark contrast between these two groups is due largely to the social context surrounding the subject of male crossdressing. For most males, dressing in women's clothing is not something to be taken lightly, and so most crossplayers choose either to take the approach of ironic humor (intentionally not passing), or that of the masquerade (attempting to pass).
Though some frown upon MtF crossplay for an immensely wide gamut of different reasons, ranging from rigid gender expectations to homophobia, MtF crossplay has become surprisingly well-accepted amidst most convention communities. Within anime conventions, bystanders typically encourage MtF crossplay, although the ways in which they express this vary.
The majority of MtF crossplayers are neither homosexual nor transgendered, though the ratio of homosexual and transgendered individuals is slightly higher within MtF crossplayers than it is with the general male public. The anime convention community is largely seen as accepting of the blurring of gender roles, and as such, may encourage some male fans to experiment with unconventional gender roles, in ways which they might not attempt outside of the convention environment.
The term genderplay crossplay could also be correctly called genderfuck crossplay, but due to the large number of minors involved in crossplay there is a consensus to use this more acceptable term
In the cosplay convention community there are a few rare individuals with majority media coverage who often misrepresent the general crossplay community by exhibiting an overemphasis on genderplay.