A sniper rifle is category weapon class that's capable of killing or inflicted major damage on an opponent, and is usually equipped with a scope.
Unfortunately, not every person can lay hands on this type of weapon. Only the Sniper Class use a sniper rifle, if you are any class other than the Sniper, you will need to get a sniper rifle from a fallen soldier if you want one, however you will not have accuracy buffs unique to the Sniper class. Or you could just play as a Sniper on your next respawn, which would probably be easier to do.
Sniper rifles possess high power, range and accuracy, but slow rates of fire and low ammo can make them hard to use in close quarter combat.
Each sniper rifle can be modified to different roles, such as long range sniping, CQC sniping, or minimum tag sniping (highest OHK rate). These include different scopes, barrels, and triggers. Sniper rifles in general have a hard time killing in CQC situations, so quickswitching is highly advised to boost ROF especially when the first shot misses.
There are both semi-automatic, automatic, and bolt action sniper rifles. Semi-automatic sniper rifles tend to do more damage than automatic sniper rifles, but have less ROF and more stability. Automatic sniper rifles, such as the VSS Katana, has high ROF and decent damage, and can OHK when the enemy has low HP. However, most automatic sniper rifles like the Dragunov SVD are 1-2 shot kill sniper rifles. They will tag a fair amount, and a OHK is not guaranteed. Bolt action sniper rifles, such as the ASW.338, M40A5, and FR-F2 all have very little tag rates due to the high damage. In some cases, such as the AWM, PGM.338,TPG1, and Blaser R93 all have modifications that can boost the damage over 100, thus reducing the tag to nearly 0%.
A list of weapons categorized as sniper rifles can be found on the Category:Sniper Rifle page.