A depeg occurs when an asset trades away from its intended peg. For a token targeting one US dollar, a price of $0.97 is 3% below the target; a price above $1 is also a deviation. There is no single universal threshold that separates ordinary trading noise from a depeg event.
Why the relationship breaks
Selling pressure, thin liquidity, reserve concerns, banking disruptions, or impaired redemption can push a token away from its target. Mechanisms based on collateral or linked tokens can also fail under stress. Prices may differ across venues, so one isolated trade does not necessarily describe the wider market.
When redemption works, eligible traders may buy discounted tokens and redeem them, helping narrow the gap. Fees, delays, limits, and uncertainty can weaken this process.
Recovery is a separate question
A depeg can be temporary or persist, and a discount is not a guaranteed arbitrage profit. Market price, stated redemption value, and what a particular holder can actually redeem are distinct.
Checking the reference asset, reserve condition, redemption rules, and executable liquidity is more informative than assuming every token labeled stable will return to its target.