What is the Impulse and why do we need it?

[Ismaël Mejía]

I have seen multiple mentions of 'Impulse' in JIRAs and some on other
discussions, but have not seen any document or concrete explanation on
what's Impulse and why we need it. This seems like an internal
implementation detail but it is probably a good idea to explain it
somewhere (my excuses if this is in some document and I missed it).