Definition
Estimate duration or cost using optimistic, most likely, and pessimistic values; the system has three sets of same-named measurement definitions (average, value selection by risk factor, PERT weighting). They measure different things and are not interchangeable.
In detail
Three-point estimating appears three times in the textbook with different formulas: the project management course uses a simple average (O+ML+P)/3 to estimate duration, the accelerated product development cost template selects one of three values based on risk factors (H takes the high value, M takes the average of high and most likely, L takes the most likely) to estimate cost, and lean software development uses PERT weighting (a+4m+b)/6. The three rule sets annotate each other; citing any one requires specifying which set and what is being estimated.
Example in practice
The team estimated the duration using three values: most likely 656, optimistic 560, pessimistic 820, taking the simple average (560+656+820)/3 ≈ 679 hours; for the same project, when estimating cost, they switched to selecting a value by risk factor—choosing M for the risk factor, taking the value as (most likely + high)/2. This is the same basis as the Accelerated Product Development cost template, not "another result that only appears on the APD page."