Rust

This is a debuff reduces armor and weapon durability effectiveness by 50% for 30 seconds. This debuff is applied to the Avatar when a monster (usually an elemental) hits the avatar with a special attack.

The rust debuff shows up as an icon under your health bar. If the "rust" debuff has been applied to you, you may consider avoiding physical attacks until the debuff expires in order to minimize damage to your gear. Also, if you can keep the elemental's stunned, they cannot apply the rust debuff because they cannot attack.