Indicates the type of interface the graphic card uses. PCI-E 2.0 gives the fastest transfer rate to the computer (2007) at 5GT/s (compared to PCI-E 1.0 at 2.5GT/s). The AGP interface is an older standard not used in new graphic cards.
Multiple GPU support meanse that you can use two or more display adapters in the same PC to speed up the graphics animation for gamers. NVIDIA's Scalable Link Interface (SLI) and ATI's CrossFire are two examples.