The high attribute in HTML is specifically designed for use with <meter> elements. The <meter> element represents a scalar measurement within a known range, or a fractional value; think of it as a gauge, such as disk usage, the relevance of query results, or a measure of confidence in a prediction.

The high attribute indicates the upper boundary of the "high" range. It sets a value that is considered to be a favorable or 'high' range for the measurement being represented by the <meter> element. Values above this threshold are not necessarily bad, but they are outside of what is considered the 'high' or 'optimal' range for the context.

In essence, when the value of the <meter> element (defined by its value attribute) is greater than or equal to the high attribute value but less than the max attribute value (or less than the max value and not specified high attribute), it suggests that the measurement is in a range considered to be high or favorable. The visual representation of the <meter> element in browsers may change based on these thresholds to give users a visual cue about the value's significance within the defined ranges.

For example, in a battery charge indicator, a high attribute might be set at 0.8 (80%), indicating that a charge above 80% is considered high or in the optimal range for battery health or usage time.

It's worth noting that the high attribute should be used in conjunction with other attributes like low, min, max, and optimum to fully define the ranges and optimal value for the measurement being represented.