Broadly, refers to different evasive actions possible using the Shield button. On the ground, fighters can dodge-roll to either side, or sidestep in place (also called an on-the-spotdodge, or spot dodge for short). In either case they’re briefly intangible, then have a little vulnerable lag at the end before fighters can act again.
Dodging backward keeps grounded fighters facing the same way. You can dash in aggressively, then dodge backward to potentially bait whiffed counterattacks; you still face forward after the dodge’s lag.
Dodging forward turns grounded fighters around. When close to a target, this is great. The dodging fighter passes through the defender and ends up at their backs, facing them. But far from targets, keep in mind that dodging forward ends with you backturned. There’s not much reason to roll forward from far away anyway (unless you’re rolling through a single incoming projectile or something).
In midair, tapping the Shield button results in an air dodge without changing air momentum. Tapping a direction on the control stick plus the Shield button causes a directional air dodge, which is like an intangible angled air dash. Angled air dodges have more lag afterward than regular air dodges.