Dodge is a layer of defence that provides a chance to prevent damaging hits.
Whether a character dodges a hit is determined by their chance to dodge, which is capped at 75%. Dodge is rolled randomly each time the character would be hit. On a successful dodge, the character does not take the hit. For this reason, dodge is handled before block and avoidance, both of which provide a chance to mitigate the damage of hits rather than preventing them outright. Dodge is not affected by the enemy's accuracy.
Sources of dodge
The only source of dodge is the Acrobatics keystone, which provides a chance to dodge spell hits by converting spell suppression into spell dodge.
|Acrobatics||Modifiers to Chance to Suppress Spell Damage instead apply to Chance to Dodge Spell Hits at 50% of their value|
Maximum Chance to Dodge Spell Hits is 75% 
Before version 3.16.0, the game had both attack dodge and spell dodge. The former is removed entirely, while the latter became a special stat only obtainable from the Acrobatics keystone. On a related note, GGG has also introduced a new layer of damage mitigation called spell suppression, which has a chance to reduce spell damage by 50% at base value.
For a detailed explanation of these changes, see Version 3.16.0 § Core Character Defences and Recovery.