Many people buy a laptop that has two graphics cards. The integrated Intel HD Graphics 3-4-5000, as well as a dedicated card. If the dedicated card is nVidia, the system typically uses nVidia Optimus to decide whether to use the integrated or dedicated graphics card at any given moment (based on resource demands and power efficiency).
The system usually dynamically switches between the dedicated and integrated GPUs, however this can cause errors and freezes in many games and applications, and the nvidia drivers regularly crash because of this.

