Thread block (workgroup)
Beginner
A bigger group of GPU workers that share a small notepad and can wait for each other.
Novice
A group of up to 1,024 threads that always runs on one GPU core, can share data through that core’s shared memory, and can synchronize at barriers. AMD calls it a workgroup.
Expert
The unit of placement on an SM. Blocks are independent, which is what lets the same kernel scale across GPUs with different SM counts. Hopper adds clusters of blocks that can address each other’s shared memory.
Explained in SIMT and GPUs (Architectures).
See also: Kernel (GPU), Shared memory (LDS).