Keyword Ability. Minions with Stealth cannot be targeted by spells or abilities from your opponents (including attacks), their attacks cannot be defended, they cannot be intercepted, and projectiles cannot hit them. Carriable artifacts carried by a Stealthed minion also cannot be targeted. Stealth is tracked with a stealth token. Stealth is lost after the minion interacts with the realm. Non-minions cannot have Stealth. If a minion with Stealth becomes a non-minion, remove the Stealth token and they lose Stealth. A minion with the Stealth keyword enters the realm with a Stealth token. If a minion becomes disabled or silenced, it will lose its Stealth token, since Stealth is an ability (similar to Ward).
Stealth is lost 'after' interacting with the realm, so here is a precise explanation of when 'after' occurs for the ways Stealth could be lost. Important note: If a minion loses Stealth for multiple reasons (e.g. activated ability that causes damage and does other things), the minion loses Stealth after the first reason. Activate a special ability: Resolve the entire ability, including any Deathrites. Once the Storyline is empty, Stealth is lost. Deal Damage: Resolve any effects concurrent with dealing damage (e.g. Daperyll Vampire gaining life based on a strike). Stealth will be lost before Deathrites resolve. Note: even if the damage is prevented (e.g. Shield Maidens), Stealth will still be lost. Strike: Resolve any effects concurrent with dealing damage (e.g. Daperyll Vampire gaining life based on a strike, or the controlling avatar losing life if a site was struck). Stealth will be lost before Deathrites resolve. Note: even if the strike is for 0 damage (e.g. Grandmaster Wizard), Stealth will still be lost. Cast a spell: Resolve the entire spell, including any Deathrites. Once the Storyline is empty, Stealth is lost.