From LQWiki

The category "Windows Emulation" includes programs that allow you to use your Windows programs in Linux. While there is often nitpicking about, or ignorance of, (depending on your point of view) the differences between emulators and virtual machines, in essence, you start an application that allows you to start non-native applications 'in' it. These basically lie to the applications and pretend to be that application's native operating system, trapping and translating requests from that program to the kernel and feeding back responses that make the application 'think' that is running on DOS or Windows or OS/2 or any number of other systems. For an end-user, this is useful to be able to run applications not available directly to Linux and, for developers, this is useful for cross-platform development.