Sill plate
The wood board bolting your home's frame to its foundation.
The sill plate (or mudsill) is the horizontal piece of lumber that sits on top of the foundation and anchors the wall framing to it. Because it's where wood meets concrete near ground level, it's vulnerable to moisture, rot, and termites. Keeping soil and mulch below the sill, maintaining good grading, and fixing leaks protects this critical structural connection.