Mercy pocket:

Mercy pocket is a slang term for a playstyle where Mercy stays closely attached to one teammate, usually a damage hero, to keep them healed and boosted while reducing their risk of being eliminated. In Overwatch 2, this usually means Mercy focuses her attention on a single ally instead of spreading healing across the whole team.

The term matters because a pocketed hero can take more aggressive positions and build pressure more safely, while the support player trades broader team coverage for stronger protection and damage amplification on one target.