AMD and Intel the graphics processors are integrated into the main processor meaning they are on the same chip basically. Discrete cards are typically made by Nvidia or AMD/ATI and they have their own memory. Integrated Graphics shares the the system memory. A machine with a discrete card is almost always more powerful since they do all the graphics processing separate from the main processor and because of this it uses more power and battery life is shorter on tasks using the discrete processor. Both ATI and Nvidia have tools that allow you to configure apps to use either discrete or integrated graphics and allow you to set a default. For most taks the integrated is enough but for gaming and image processing a discrete card makes life easier.