Micro is a RTS term for how well you control your units. In starcraft for example you have the unit "stalker", which can teleport. Professional players with very good micro can use that teleport to always teleport out a Stalker just before it would die. This means because of good micro they don't lose their units.

The opposite is macro, which mainly talks about how good a player is in managing the game on a grander scheme like managing their resources and having an overview over the whole map

(I hope my example is still accurate it has been years, that I watched an rts game)

It just means having to micromanage a particular unit's actions. I like it more when I can say "patrol this area, return fire and advance a bit if necessary, but no further than this", instead of having to flip back to those units constantly to manage them. IMO it's more thematic anyways for a sci fi game, you're probably going to have units with a basic AI in them in-universe.