What makes a return good, and what do "down", "out" and "not up" mean?

Question

Accepted Answer

A return is good if the ball (World Squash Singles Rule 6.2):

is struck correctly (with the racket held in the hand, once, without prolonged contact) before it bounces twice;
hits the front wall, directly or off other walls, above the tin and below the out-line, without bouncing on the floor first, and without hitting either player, their clothing or racket;
doesn't touch the tin on the way back; and
isn't out.

The marker's calls when it isn't:

Call	Meaning
Down	Hit the tin, or the floor before the front wall, or the front wall and then the tin
Out	Hit a wall on or above the out-line, any fixture above it, or the top edge of a wall, or went out of the court or through a fixture
Not up	Not struck correctly, bounced twice before being struck, or touched the striker or their clothing

Note that a ball touching the out-line is out, and the tin counts as down.