PID controller (P/I/D)
The PID controller is the algorithm Betaflight uses to hold your quad on the commanded rate: P reacts to the current error, I removes steady-state drift, and D damps oscillation and overshoot.
In a blackbox log, PID behaviour shows up as how well the gyro (actual) tracks the setpoint (commanded). PIDoctor measures this per axis via the step response — rise time, overshoot, settling — and turns weak tracking into concrete P/D/I CLI suggestions.