M.2 heatsink
A heatsink (often a metal plate with a thermal pad) mounted on an M.2 SSD to keep the temperature down. Increasingly important as PCIe 4.0 and especially 5.0 NVMe drives get so hot that they throttle the speed (thermal throttling) without cooling.
Problem: fast NVMe controllers (PCIe 5.0, 14 GB/s) generate a lot of heat on a small area; if the controller gets too hot it lowers the speed to protect itself → performance dips in the middle of large transfers. A heatsink leads the heat away and holds the drive's peak speed longer. Modern motherboards often ship with built-in M.2 heatsinks; PCIe 5.0 drives may even require active cooling (a small fan). Trade-off: the extra height can clash with graphics cards/coolers. Distinct from the NAND cells' needs (they actually do well with heat) — it's the controller that must be cooled. Related to M.2 slot and thermal throttling.