What is Wine?
Wine is awesome. No, I'm not talking about the kind you drink, I mean the kind that lets you run Windows apps without the Windows operating system. It's kind of Zen, when you think about it. Oh, and did I mention it's completely free, legal, and open source?
Nowadays, Windows and Mac play nicely together. You can install Windows and Mac side by side and switch between them using Boot Camp, but that requires a reboot every time, and you can only use one operating system at a time. You can also use a tool like Parallels Desktop or VMware Fusion to virtualize Windows and run it together with Mac, but virtualization is slow and it takes up a lot of memory. (Your physical computer creates an imaginary "virtual" computer within itself, and runs Windows on that. That takes a lot of resources!) On top of that, all of these solutions require you to own a legal copy of Windows, which isn't cheap!
Wine is different. When any program runs, it requests resources like memory and disk space from the operating system. All that Wine does is make sure that those requests get answered so that the program can run correctly. As far as the program knows, everything is going smoothly because it has everything it needs. It never even realizes that it's not running on Windows! It's simpler than emulating a whole new computer, so it's faster. Since it's just translating requests, you don't need a copy of the actual Windows operating system. Plus, Wine is open source, which means people are continually improving it and adding new features. And you can't beat the price!
(Copy-Paste from http://www.davidbaumgold.com/tutorials/wine-mac/)
Wine Official Site: https://www.winehq.org/
Wine official source release site: http://sourceforge.net/projects/wine/files/Source/