It's used in many words related to government, society, and the organization of a community:
* Politics: the activities associated with the governance of a country or other area.
* Police: a civil force responsible for maintaining order and enforcing the law.
* Policy: a course of action adopted and pursued by a government, organization, or individual.
* Polity: a form or system of government.
* Metropolitan: relating to a large city.
* Politician: a person who is actively involved in politics, especially as an elected representative.
So, whenever you see "poli" in a word, you can usually expect it to be related to the concept of a city, state, or community.