There seems to be no official name for this handy technique that kills running apps and clears RAM (memory). This often fixes mis-behaving audio and MIDI apps and is quicker than powering down or forcing a completely restart.
It is useful to do before starting a music session or if you run into problems that might be caused by memory leaks or zombies.
See also: Hard and Soft Reset
TIP: Via the accessibility settings, set your 3 power button click shortcut to bring up (and then re-hide) the virtual home button. With this set up you can do a memory clear with a 2018 Pro in under 10 seconds.
(thanks to @Ocelot and @aplourde and @marmakin)