Enemy sniper is a hostile marksman that's hidden somewhere, trying to blow the player character's face off from afar. These enemies don't move around a lot but are a pain to find as they are usually camouflaged and well hidden. They often have the advantage as they can sometimes pick you off in one shot without you even knowing that the enemy was there. They like to hide near windows, in tall grass or somewhere that gives them a nice view of what is going on around them.
Enemy snipers aren't invincible though. Multiple things can give away their location. First of all, if not silenced their weapon makes a really loud noise that can tell the player in which general area they are hiding. Also some snipers have lasers attached to their gun for aiming purposes. This always tells the player where they are hiding. Also if they're facing in the right direction they can see a small flash of light right before they fire (this is in fact the reflection of light against their scope) which tells them exactly where they're hiding. Enemy snipers sometimes have a shotgun or an SMG as a secondary weapon for close encounters meaning that they are both deadly from afar as well as up close.