What's the difference between AVO and DDG?

When providing battle support, units offer AVO, which is Avoidance. I know it directly lowers enemy's chance to hit.

But units can also increase DDG. I can't find anything in the in-game help about what it does, or what it stands for. Presumably, it's meant to be short for Dodge, but I've seen supports offer both AVO and DDG, which leads me to believe that's not what it is.

What is DDG, and what does it do? If it differs from AVO, what is the difference?

You are right that DDG is short for Dodge. It's similar but different then Avoid.

Avoid is used to avoid/dodge Normal hits, like you stated correctly. With higher AVO you have a lower chance to get hit at all.

Dodge is used to avoid/dodge Critical hits. So with an increased Dodge, you have less chance to get critical hitted, while NOT reducing the chance to get hit at all.