Recoil Lug
The flange that anchors the barreled action to the stock and transfers rearward recoil force into the bedding rather than the action screws alone.
A recoil lug is a steel flange, either integral to the receiver or sandwiched at the barrel joint, that gives the rearward thrust of firing a solid surface to push against. Without it, recoil would load only the action screws, so the lug spreads that force into the stock and keeps the action from shifting under repeated shots.
For accuracy the lug must seat squarely and consistently against its recess. Quality bedding supports the lug fully on its rear face so the barreled action returns to the same place after every shot, which protects zero. A loose, partially supported, or canted lug is a common source of vertical stringing and wandering point of impact in an otherwise sound stock.