"A person who is active duty is in the military full time. They work for the military full time, may live on a military base, and can be deployed at any time. Persons in the Reserve or National Guard are not full-time active duty military personnel, although they can be deployed at any time should the need arise."
The Guard is different from the Reserve in that their chain of command is through the State governor. They can be federalized, but they are the only "troops" that a governor can control. Frequently see them used during natural disasters. Reserves can't do that.
May seem subtle, but an important point for DOD to keep federal forces from being active on US soil. Any deployment in the US will be a Guard unit.
This was part of the issue for DOD brass in calling up the DC Guard to go to the Capitol. They are the only Guard under direct control of POTUS (because DC is not a state, they do not have a governor) so always federal. That would have been federal troops vs US citizens in a political fight.
(yes there was probably more going on - but that was part of it)
My local Guard unit are actually helping out in my health department right now with COVID vaccines. They are handling the "processing and paperwork" so all nurses are freed up to give the vaccine. Local additional
man err human power is a big part of the job.