Barrier
Barrier soaks up damage before any of it reaches your HP. Items like Aegis Shard hand you some at the start of every battle, and whatever you spend stays spent until the next fight begins.
In detail
Barrier is spent before any damage reaches your HP. It refreshes at the start of every encounter from your charms, which stack linearly across copies. It lasts that encounter only: it does not carry between fights and is not saved. Freyr's Sumarbrandr's Ward builds barrier on any match up to a cap, where the Lucky Stone charm pays only on Earth matches, and every point his barrier absorbs feeds his ability bar.
More in glossary
From the current development build. Content and balance may change before release. This public reference includes discoveries and does not reflect your personal unlocks.