Leaning

In first-person shooter games, leaning is a game mechanic that allows characters near corners or other cover to lean around the cover. This reduces or eliminates exposure of the shooter's feet, legs, and torso, which the target may use to counterattack.

Battlefield 4
Battlefield 4 includes a "context-sensitive" leaning system (borrowed from Medal of Honor: Warfighter). The system is activated by standing near appropriate cover; the soldier actually leans when the button is pressed.

The leaning system also distinguishes between vertical cover (e.g. building corners) and horizontal cover (e.g. window sills), allowing the soldier to lean to the side or peek above as appropriate.