Burr (burl in the US) is a specialty wood product that typically comes from tree crotches, roots, or areas with some kind of damage. It is relatively rare compared to ordinary wood, so it is more expensive than non-burr wood of the same species. In veneers, it can be very fragile, sometimes with voids, that can make it more difficult to work with.
Only pretty high-end cars typically came with true burl in the interiors.
Ed