The term refers to rail-based systems that offer flexibility and consistency. Instead of installed recessed lighting or permanent fixtures, track lighting gives you a single line along which you can place lights in any configuration. Bunch them together at one end, space them evenly throughout or create something of a hybrid to match the art on your walls – it’s your choice. Most systems can be adjusted quickly with little more than a stepstool and a manual twist, offering modular and flexible options on a daily basis. You may even want to switch the lighting scheme as you change the rest of your room around – a cinch with today’s simple fasteners. One of the great advantages of track lighting is that the lights can be controlled individually or en masse.

If you want a romantic ambiance and spot lighting, you can select one or two bulbs and leave the rest dormant. Conversely you can set a wall into dazzling brilliance simply by lighting the full array at once – a breathtaking effect with the proper hanging pieces. Enterprising homeowners occasionally even swap bulbs out to create something of a staggered effect, keeping some brighter and the rest at a cooler burn.

Source: http://homeimprovement.superpages.com/lighting/track-lighting-in-the-home.html 

More details of track lighting