What is it called where the ceiling meets the wall?
Keeping this in view, what is it called where the wall meets the floor?
In architecture, a baseboard (also called skirting board, skirting, mopboard, floor molding, or base molding) is usually wooden or vinyl board covering the lowest part of an interior wall. Its purpose is to cover the joint between the wall surface and the floor.
Then, how do you fill a gap between a wall and a ceiling?
Cover the mesh tape with drywall joint compound, using a putty knife. Press the joint compound firmly into the small mesh holes of the tape, covering the mesh tape completely. Extend the mud beyond the borders of the tape about two inches on both the wall and ceiling surfaces.
Neither caulk nor shoe moulding are mandatory. They are aesthetic decisions and both are used to typically cover gaps. If you don't like the gaps, use them. If the gaps aren't there and don't bother you, no biggie.