Estimate
Also: engineering estimate, approximation
A deliberately simplified, bounded answer used to guide a decision before exact data exist.
An estimate states assumptions, scale, uncertainty, and validity range; it may combine models and measurements without claiming exactness.
Example A 10 Wh source driving 2 W has an ideal runtime near 5 h before losses.
Common misconception An estimate is not a guess and extra decimal places do not make rough inputs precise.