The term "B.A.R." in the context of a propeller typically refers to "Blade Area Ratio." This is a measure used to evaluate the efficiency and performance characteristics of a propeller. The Blade Area Ratio is calculated by comparing the total area of the propeller blades (the effective area that contributes to generating thrust) to the area of the disk that the propeller would sweep out when it rotates.
The formula for Blade Area Ratio (B.A.R.)