The Cover System is a gameplay mechanism that appears in Watch Dogs.
Players have the ability to take cover behind objects or environmental elements that are nearby. When engaged with, or tailing a potential victim/criminal, a player will have the ability to quickly take cover behind anything that is large, dense enough and in their direct line of sight. When the camera is facing an applicable object/environmental element, the player can press "X" (PS3 and PS4) or "B" (Xbox One and Xbox 360) to quickly take cover.
Taking cover allows a player more time to come up with an attack strategy or to regenerate health. Taking cover can also help a player avoid taking too much damage from enemies armed with guns. The cover system can also be used as a means of efficiently disposing of hostile targets; waiting behind cover for a moment when an enemy is not firing and can be easily killed.