Hanging square and deflection tactic leading to a back rank checkmate [FEN "2r1r1k1/5ppp/8/8/Q7/8/5PPP/4R1K1 w - - 0 1"]


The important square of e8 square is hanging. It is hanging because if white can take that square it's checkmate. Is this a hanging square tactic?

If the rook on Rook on c8 is deflected from the  protection of e8, is it called a deflection tactic?

[FEN "6k1/3qb1pp/4p3/ppp1P3/8/2PP1Q2/PP4PP/5RK1 w - - 0 1"]


Here, the important f8 square is not hanging, so white plays Qf7+ to deflect the king from protection of f8 square, thus leading to checkmate.
I haven't heard of the term "hanging square" before. But you're right that the c8-rook would be deflected (or "attracted") if it were taken away from defending the rook on e8.