Unless you are a hermit (like my husband wishes to be, but I won’t let him), you have to deal with people. The word “people” has long been used to refer to an uncertain quantity or indefinite number of human beings (uncountable). “Persons” has been used when referring to a definite number of homo sapiens (countable).
They are expecting a lot of people at the Marcellus Shale town hall meeting.
However, occupancy of the room is limited to 84 persons, according to the fire marshal.
Some style books, including the AP book on my shelf, prefer the use of “people” to “persons” as the standard plural of “person,” even for countable instances.
Fortunately, only 81 people showed up for the town hall meeting, so we didn’t have to turn any away.
People can also be singular, as in the case where it acts as a collective noun that means “race or nation.” In such circumstances, “people” takes a plural verb.
The American people have a special fondness for freedom.
This particular meaning of “people” can also be used as a plural, as in “peoples.”
Many peoples, tribes, and nations have a story or legend about a Great Flood that destroyed all but eight persons.