Quadro is Nvidia's line of workstation graphics cards for professional applications. They actually tend to have LESS raw computing power than the GeForce gaming/general purpose graphics cards, but they are more expensive because 1) they include a higher level of tech support; 2) they have drivers optimized for a number of popular 3D, CAD, and other professional software applications, and 3) they sell in far fewer numbers than the mass market cards. These workstation graphic cards are great if your profession includes 3D animation, modeling, architectural rendering, CAD, or complex mathematical computations, as they will give superior performance with the software they're designed to work with.
They are not even worth worrying about if your main focus is games, or even Adobe Photoshop. Even if you are a graphics professional, be sure to only buy a workstation card if it improves the performance of your main application(s). The workstation card reviews here on Tom's will help you determine that.