A dab mat (also known as a dab pad) is a mat placed underneath a dab rig in order to protect the surface from any residue that may drip off the dab nail.
He put the dab mat on the table underneath the rig before dabbing.
The dab mat kept the waxy residue from getting on the table.

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What is a dab mat for?
The primary purpose of dab mats is to protect the surface, like a table, from dripping residue. A dab mat also cushions a rig from scratching or breaking, and it can be a great place to put your dabber when it's not in use.
More about dab mat
When you add concentrate to a hot dab nail, a sticky or waxy residue may drip off the end. If this residue gets on any surfaces — for example, a wood table — it can be hard to remove.
Dab mats stop any wax, oil, or other dab-related residues from ruining the surface underneath your dab rig. Some dab mats are padded in order to offer additional protection for the dab rig; should the dab rig accidentally fall over, a padded dab mat can help prevent breakage.
In terms of appearance, there's no one-size-fits-all dab mat. They come in a variety of shapes, sizes, and materials. Dab mat variety has become such a staple in the dab scene that some people have large collections of dab mats to coordinate with other accessories in their setup.
Ideally, a dab mat will be large enough to easily cover the surface area underneath a dab rig, and to provide additional space for spreading out nails, concentrates, and any other dabbing accessories. Most dab mats are made of materials that are easy to clean, such as rubber or silicon. They can be plain or feature custom artwork or other designs.
Dab mats can easily be purchased online from major retailers or specialty cannabis sites, and many dispensaries will have a selection of dab mats for purchase in store.
How do you clean a dab mat?
As mentioned, most dab mats are made out of easy-to-clean materials and should clean up with soap and water. If you have a lot of buildup on a silicone dab mat, you can also scrub it with a paste of baking soda and warm water before rinsing.