Thrust refers to the force exerted by the rotating propeller in the direction of travel of the airplane. This is the whole purpose of the propeller - to convert the power of the engine which appears as a rotating force, or torque, into a linear force to propel the airplane. Thrust is usually measured in pounds is a function of air density, rpm, diameter, advance ratio and Reynolds number. It is a long, complicated process to get this number, but what is important to remember is that thrust is different for every shape of propeller and changes with flying conditions. Power Absorption refers to the power output curve of the engine.
Power is the product of torque times rpm.
This is why a power curve becomes flat or decreases at higher rpm's, and means that the most efficient propeller is the one that allows the engine to operate at its optimum power band. An interesting point in understanding power absorption is that propeller power varies as the cube of the rpm. Consequently, twice the rpm requires 8 times the power. Tip Speed is measured in feet per second and a formula is provided below to find this measurement. For model airplane purposes, the best tip speed for efficiency and noise requirements is 600 feet per second.