What does it mean when a pump stalls? I could not find a useful explanation with the search terms pump stalling and hydraulic pump stalling. I'm trying to understand what Elon's tweet means. Maybe an animation could help but checking the videos section with these search term also didn't help me.
A stalled hydraulic pump is one the following:
its outlet is blocked, to allow measurement of it maximum outlet pressure under stalled conditions
a pump which has stopped delivering flow because of flow separation and cavitation on the impeller blade(s)
Elon's tweet refers to the second definition.
Hydraulics stalls of compressors may have been the cause, although the term stall has a wide range of use.
Jet engines at the early times could stall by disruption of flow around compressor blades exactly in the same way as an airfoil can stall, and it starts by a small pocket of air stalling around a few blades and the air turning with the compressor blades as opposed to being pushed forward.
It was later corrected by modification in the design of jet engines and digital engine controls.
If you already know the more about the case it would help, otherwise a pump stalling could mean many things, not the least of which the political angle Musk may have had.