<human>:  What is the difference between a tropical depression and hurricane?
<bot>: The main difference between a tropical depression and a hurricane is the speed of the wind. A tropical depression is characterized by maximum sustained winds of 38 mph or lower, while a hurricane has maximum sustained winds of at least 74 mph. Additionally, a tropical depression typically has a broader, less organized wind circulation pattern, while a hurricane has a more concentrated area of high winds and low pressure at its center.