What is the word for the corner where ceiling and wall meet in a house?

The terms ceiling line and floor line are used for the lines where the wall meets the ceiling and the floor, respectively. For example, the terms are used in the book Architectural Drafting for Interior Designers (by Lydia Sloan Cline):

To make it more clear, I drew this diagram in Paint:

You can use the term cove or coving for the concave arched molding at the junction of a wall with a ceiling.

The definition of coving from britannica.com:

Coving, in architecture, concave molding or arched section of wall surface. An example is the curved soffit connecting the top of an exterior wall to a projecting eave. The curve typically describes a quarter-circle. The arched sections of a curved ceiling would be coving. Such a coved ceiling serves to join the vertical walls with a flat ceiling.

The definition of cove from Architect's Illustrated Pocket Dictionary (by Nikolas Davies, Erkki Jokiniemi):

1 a curved underside or soffit

2 coving; a concave moulding of plaster, timber or plastics, fixed as a decorative covering at the meeting of ceiling and wall; any meeting of ceiling and wall treated in this way; a cove tile; see also cavetto.

Note: In North America, the term crown molding is used for the molding at the junction of an interior wall and ceiling.

The cornice area is where walls and ceilings join.

From Home Design Directory