The highest trading price a digital asset has ever reached. It is common practice to keep a currency's ATH in mind when trading, as it represents an important psychological and technical price level of interest to the market. Approaching or surpassing the ATH can trigger increased volatility as traders take profits while breakout traders look to ride the momentum higher.
Example
“Bitcoin's ATH became a key resistance level, and traders watched closely to see whether it would break through or reject.”