This is the SPU's local store. It's mentioned in the article. More details at https://en.wikipedia.org/wiki/Cell_(processor) Apparently it could in theory go to 4GiB.

"The local store does not operate like a conventional CPU cache since it is neither transparent to software nor does it contain hardware structures that predict which data to load."

I think the general term for this is scratchpad memory. https://en.wikipedia.org/wiki/Scratchpad_memory

This kind of indicates the problem with it. When switching tasks, each local store would have to be put into main RAM and the new task's local stores pulled back out. This would make switching tasks increasingly expensive. I believe the PS3 (and maybe all cell processors) dealt with this by not having tasks switch on the SPUs.