Final answer:
The P wave on an ECG tracing represents depolarization of the atria.
Step-by-step explanation:
The P wave on an electrocardiography (ECG) tracing represents depolarization of the atria. It is a small wave that indicates the beginning of atrial contraction. The atria start contracting approximately 25 ms after the start of the P wave.
The P wave is followed by the QRS complex, which represents the depolarization of the ventricles and the beginning of ventricular contraction. The T wave, on the other hand, represents the repolarization of the ventricles and marks the beginning of ventricular relaxation.
So, in summary, the P wave on an ECG tracing represents depolarization of the atria.