If I can describe the subspaces of R^3 as being lines, planes, all of R^3, and the zero vector then how can I describeDthe space of all 2x2 diagonal matrices?

Would it be correct to say: a "line" of 2x2 diagonal matrices, a "plane" of 2x2 diagonal matrices, all ofD, and the zero matrix?

Is there a term for a "line"/"plane" of matrices?

Is there a term for a "line"/"plane" of functions?