Definition
Two related left-turning tendencies caused by a single-engine propeller airplane's powerplant. Torque is the reaction force that tries to roll the airplane in the opposite direction to the propeller's rotation; in most U.S.-built airplanes the propeller turns clockwise as seen from the cockpit, so the airframe tends to roll left, which the wheels translate into a left yaw on the ground and a left-rolling tendency in flight. P-factor (asymmetric propeller loading) occurs when the airplane is at a high pitch attitude or high angle of attack: the descending propeller blade on the right side bites into the air at a greater angle than the ascending blade on the left, producing more thrust on the right and yawing the nose to the left. Both effects are strongest at high power and low airspeed -- exactly the conditions of takeoff and initial climb -- and are countered with right rudder.
Plain English
When you apply takeoff power, the airplane wants to swing its nose to the left. Two things cause this: the engine's twisting force pushing back against the airframe, and the propeller's right-side blade taking a bigger bite of air when the nose is pitched up. The pilot uses right rudder to keep the nose pointed straight down the runway.
Context Anchor
Seen during normal takeoff, especially when discussing common errors such as failing to keep the airplane tracking straight down the runway.
Derivation
Torque comes from the Latin 'torquere,' meaning 'to twist' -- which is exactly what the engine is doing to the airframe. P-factor is short for 'propeller factor,' a term coined to describe the asymmetric loading of the propeller disc when the aircraft is not flying directly into the relative wind.
Why Pilots Care
Without correction the aircraft will drift left off the runway centerline, especially at high power settings.
Analogy
If you push hard on one side of a shopping cart handle, the cart wants to turn instead of going straight. Torque / P-factor is not the same force, but the result is similar: the airplane needs a correction to keep moving straight.
Grounding Statement
Picture adding full power for takeoff and feeling the nose want to move left unless you hold enough right rudder.
Intuition Check
Do not treat torque / P-factor as one vague “engine pull.” Torque is a twisting reaction from the engine and propeller; P-factor is uneven propeller pull in a nose-up, high-power condition.
Example Sentence 1
As the throttle came up for takeoff, the student felt the nose swing left and quickly added right rudder to counter torque and P-factor.
Example Sentence 2
At full power with the nose high, P-factor and torque effects increase and require continuous right rudder pressure.