Thought is the operation of the brain in conscious activity. It may or may not be goal-directed, aimed at solving specific problems. It is not the only way brains operate. Behaviour may occur as a result of instinct, and the adaptive unconscious may solve problems without a person being aware.
Other animals can use their brains to solve problems, but there is no way of telling whether they do so consciously. Thought is investigated by four or five academic disciplines, each in its own way. The disciplines include psychology, philosophy, biology, physiology, psychoanalysis and sociology.