"Duty" has a few different meanings, depending on the context:
* Moral obligation: This is the most common meaning. It refers to a responsibility or obligation that we feel we should fulfill, often based on our moral principles, social norms, or legal requirements. For example, you have a duty to care for your children, or a duty to pay your taxes.
* Military service: In this context, "duty" refers to the time spent on active military service.
* Task or work: This is a less common usage, but "duty" can refer to a specific task or job that someone is assigned. For example, a police officer might be assigned to "traffic duty".
If you provide more context or an example sentence, I might be able to give you a more specific answer!