What is the difference between supplication (du'a) and reliance (tawakkul)?

Trust in Allah is: confidence in what is with Allah and cutting off greed for what is in people's hands. It is not complete except by taking the necessary means. As for supplication, it is: the servant's calling upon his Lord for care, seeking His help, and manifesting his destitution before Him. It is one of the means by which the servant attains his objective. There is no contradiction between supplication and trust in Allah; for supplication is one of the means without which trust in Allah is not complete.