[willis936]

As someone else said, this is superscalar, though these days companies refer to the number of concurrent out-of-order pipelines as Execution Units (EUs).

SMT is a second set of registers that uses the same execution hardware. If a thread stalls waiting for a main memory read then the other thread can jump in after the pipeline is cleared out (or maybe before if you're clever and careful, but idk if this is done in practice). You can also impose some governance over time sharing so threads with low data memory footprints don't lock out other threads.