From the website:
Minecraft is a game about breaking and placing blocks. At first, people built structures to protect against nocturnal monsters, but as the game grew players worked together to create wonderful, imaginative things.
According to Wikipedia (as of April 19, 2015):
Minecraft is a sandbox independent video game originally created by Swedish programmer Markus “Notch” Persson and later developed and published by the Swedish company Mojang. The creative and building aspects of Minecraft allow players to build constructions out of textured cubes in a 3D procedurally generated world. Other activities in the game include exploration, gathering resources, crafting, and combat. Multiple gameplay modes are available, including survival modes where the player must acquire resources to build the world and maintain health, a creative mode where players have unlimited resources to build with and the ability to fly, and an adventure mode where players play custom maps created by other players.
Minecraft is available in a number of languages: English, Danish, Dutch, Spanish (General & Mexico), Finnish, French (General & Canada), Italian, Japanese, Korean, Norweigan, Polish, Portuguese (General & Brazil), Russian, Swedish, Chinese (Simplified & Traditional).
Minecraft was acquired by Microsoft Corporation in 2014 and developed by Mojang, now functioning as a subsidiary of Microsoft.