Bulkheads and stringers stiffen a hull, and tabbing is what holds them to it. It's fibreglass cloth and resin laid over the joint on both sides, lapping onto the bulkhead and onto the hull.
Dave Gerr, writing for Good Old Boat, explains that tabbing makes a secondary bond, laid onto laminate that has already cured, and that it's never as strong as a primary bond. Done well, the surface is ground, cleaned and given a fillet in the corner. Done badly, it can be pulled off by hand.
What a surveyor checks
Follow every bulkhead and stringer you can reach where it meets the hull. Look for tabbing that's lifted, cracked or separated, and tap along it: a hollow sound means the bond has let go. Then look for what loose tabbing causes, such as doors that bind and a chainplate bulkhead that shifts when the shroud is loaded.
In the report
"Main bulkhead, port side, tabbing separated from the hull for about 400 mm below the chainplate, hollow when sounded, bulkhead visibly moves when the cap shroud is loaded. Structural. Grind back and re-tab before the rig is loaded." See loose bulkhead tabbing.