Shared memory (LDS)
Beginner
A small, fast notepad inside each GPU core that a team of workers can share.
Novice
Fast on-chip memory inside each GPU core that the programmer controls directly. Threads in the same block use it to share data and to reuse it without going back to main memory. AMD calls it the local data share.
Expert
A banked, software-managed scratchpad (32 four-byte banks on NVIDIA) carved from the same SRAM as L1 on recent NVIDIA parts. Bank conflicts serialize accesses. It is the staging area for GEMM and attention tiles.
Explained in SIMT and GPUs (Architectures).
See also: Scratchpad memory, SRAM (static RAM).