A shunted tombstone is a light socket that has 2 electrical contacts which are internally joined to create a single path for an electrical current to pass through.
The term tombstone refers to the shape of the socket and provides a track from the ballast to the lamps pins.
Fluorescent light fixtures such as the T5 and T8 fluorescent fixtures have the shunted tombstone sockets.
Shunted sockets are light sockets that house internally connected electrical contacts.
The electrical current in a shunted socket runs on a single track from the ballast, through the socket, and then to the lamp's pins.
These types of sockets receive their voltage through a single set of wires and spread it to two contacts.
If you have shunted tombstone sockets, you will need to rewire or replace them and connect them to match the single-ended LED tube light manufacturers' wiring diagram.
If your LED tube light is double-ended, it is likely compatible with both shunted and non-shunted tombstones.