A dacha is a country residence (typically a small cabin without the comforts those of us in western civilization take for granted: like indoor plumbing) where Russians go during hot summer weekends, escaping the cities for a real getaway from apartment life, which is the rule in Russian metropolitan living.

Moscow Life has a couple of informative, interesting articles about dachas. This site is authored by a real Muscovite, and includes a lot of information from a native's viewpoint.