From what I've seen, people refer to LEFT SWING or RIGHT SWING based on the side of the body that the swing is held on before release of the attack.
LEFT SWING = weapon is held across the player's body on their left side, releases from their left to their right
RIGHT SWING = weapon is held on the right side of the player, releases from their right to their left
The problem arises when people refer to swings based on how they initiate the action (i.e. mouse movement).
This is a problem because there are two types of mouse movement (normal and inverted) for dictating attack direction. As the names suggest, you would move your mouse in completely opposite directions to perform the same attack.
I only brought up the issue because a previous poster actually referred to the incorrect attack direction (based on context of what the poster was addressing). Yes, normally "left swing" and "right swing" are taken to mean where the weapon is held relative to the body, but when
people start referring to the opposite direction because they're going by how they move their mouse, then the only solution is to be as specific as possible. Rereading the post just makes me think that that poster had no idea what he was talking about.
Apologies for the side-bar.