What does PID stand for and what does each term do?

PID stands for Proportional-Integral-Derivative. Proportional (P): output proportional to error - provides immediate response, cannot eliminate steady-state error alone. Integral (I): output proportional to accumulated error over time - eliminates offset, but can cause overshoot. Derivative (D): output proportional to rate of change of error - anticipates future error, provides damping, reduces overshoot. Together: P provides basic response, I eliminates offset, D improves stability. Most common algorithm: CO = Kp*(e + 1/Ti*integral(e*dt) + Td*de/dt).