Your view is 'teleported' behind enemy player where you can shoot, knife, nade them.
This quite a decent explanation, but rather than being behind the enemy, you are actually 'attached' to the player.
This is an extensive description of telekilling taken from a source.. "Telekill is, in function, a reverse-OPK. Instead of bring the enemies to you, your camera is locked directly in front of your target. You will see them and beable to shoot them, knife them, or even throw nades around them but they will not see you."