Backcountry - Cross Country Skis are best used for breaking your own trail and seeking out your own adventure. Backcountry Cross Country skis are typically shorter, stiffer, stronger and wider. Having a shorter ski will allow you to have more maneuverability when cruising through the woods. A stiffer and stronger ski is required because you will be breaking your own trail, and these skis will deliver more power in the deep snow. Having extra width will provide you with more surface area to allow you to stay on top of the snow to move faster, easier and more efficiently. Backcountry Cross Country Skis typically have metal edges as well. Metal edges will give you more support and control on short downhills, and will give you a firm grip on the snow as you traverse across a slope.
Groomed - Cross Country skis that are designed best for use on the groomed tracks have scales on the bases that provide you with traction as you glide down the track. Skis that are used for the groomed tracks are often referred to as the Classic skiing style. The Classic skiing style is done by putting one foot in front of the other to push, and using your poles to help propel you down the track. Skis used on the groomed tracks are typically narrower to aid in mobility and faster gliding. These are the most popular style of cross country skis.
Groomed/Ungroomed - Cross Country Skis are most commonly used on the groomed tracks, but do offer wider tips and wider waist widths that will offer you more support and stability on the ungroomed terrain, but are not as wide as Backcountry skis. Groomed/Ungroomed skis are still narrow enough and agile enough to glide fast and efficiently on the track.
Skate - Skating Skis are the speed demons of the cross country world. The Skating skiing style can only be done on groomed tracks and mimics the motions that you see in ice skating or inline skating speed events. Skating skis are typically stiffer and shorter than other types of Cross Country Skis. Skating skis need to be stiffer to give you the push and propulsion that you need to move at faster speeds. These skis are also shorter to make them more maneuverable, and allow you to make longer strides. These types of skating skis usually have a high amount of camber underfoot to improve the amount of push you get with each stride. The bases of Skating skis require wax, so you can fine tune your speed to the snow conditions and temperature range.