Bonenkai or "Forget the Year Parties" and Shinnenkai or "New Years Parties" are held in Japan. Typically Bonenkai are held in December, and Shinnenkai are held in January. Usually not celebrated with family, these two distinct types of parties are held among friends, students, and coworkers. Shinnenkai should not be confused with Shogatsu, which is the traditional "New Years" holiday (typically held January 1 through the 3), and which is usually spent with family. Both of these parties are normally thrown at restaurants, though sometimes bars. Typically companies throw these affairs for their employees, (much like a Company Christmas Party™), people go to a Izakaya for food. By definition, Izakayas sell small to medium sized dishes, and serve drinks, catering to those who aren't very hungry and are looking to hang out with their coworkers for a few hours before going home. Not completely unique to Japanese culture, in fact, probably all cultures have the "hanging out with people you like" or the "hanging out with people you work with" thing, this is simply what it's called and who participates, typically.
http://www.japan-guide.com/topic/0101.html