MBS

From The StarCraft 2 Wiki

Multiple Building Selection, also known as MBS has been a hot topic for StarCraft II even since it was first mentioned that the game could select and group buildings, and not just units. The reason for the controversy is that it lessens the weight of micromanagement in gameplay, and in some people's opinions, it "dumbs it down".

Blizzard are currently having MBS in StarCraft II, and are unlikely to remove it. They have made changes to how the building of units work though, making a player still do multiple keystrokes if he wants to make several units in multiple buildings. One press per unit per building. This means that with 10 Barracks with attached reactors, a player would need to press "M" 20 times to make Marines in all slots for production.

The opposite attribute to MBS is "SBS" - Single Building Selection".