A quote is stale when the price on the screen no longer reflects the market it came from. It happens whenever there is a delay between the price being formed and the price being displayed or acted on: a slow connection, an overloaded feed, a platform that has stopped updating, or simply a market moving faster than the refresh rate.
Stale quotes matter in both directions. Acting on one means sending an order at a price that has already gone, which is where rejections, requotes and unexpected slippage come from. Being on the other side of one is why brokers and liquidity providers apply latency checks and price tolerances, and why deliberately trading against known-stale prices is treated as abuse in most client agreements rather than as a clever technique. A frozen chart, a spread that stops moving in an active session, or a ticket price that will not change are the usual signs to check the connection before trading.
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Guide
How to Read a Volatility Quote
A volatility number is a price for uncertainty, not a prediction. What it measures, why one pair has many of them, what the shape is called, and where the figures actually come from.