Queen's Pawn Game
Chesspedia, the Free Chess Encyclopedia.
In the most general sense the term Queen's Pawn Game can refer to any chess opening which starts with 1.d4, the second most popular opening move, but is now usually used to describe openings where White opens with 1.d4 but does not follow through with an early pawn advance to c4. Some of these openings have individual names as well, e.g. the Trompowsky Attack, Torre Attack and Stonewall Attack.
In the 1800s and early 1900s, 1.e4 was by far the most common opening move by White, while the different openings starting with 1.d4 were considered somewhat unusual and therefore classed together as "Queen's Pawn Game".
As the merits of 1.d4 started to be explored it was the Queen's Gambit which was played most often; more popular than all other 1.d4 openings combined. The term "Queen's Pawn Game" was then narrowed down to any opening with 1.d4 which was not a Queen's Gambit. Eventually, through the efforts of the hypermodernists, the various Indian Defences, such as the King's Indian, Nimzo-Indian and Queen's Indian, became more popular, and as these openings were named, the term "Queen's Pawn Game" narrowed further.
In the Encyclopedia of Chess Openings, most Queen's Pawn Games are classified early in the D-volume (D00-D05) if Black responds to 1.d4 with 1...d5. If Black does not play an early 1...d5 the opening will be classified in the A-volume.