there are several points to make here. The first one os to do with singular and plural nouns, I'm sure you know that most nouns in English are made plural by putting and s on the end, so for example, girl – girls, boy – boys. But some nouns have irregular plurals, for example child – children. And 'person' is one of those nouns that has an irregular plural. 'People' is in fact the plural form of person. So for example we talk about one person and two people. So in normal everyday speech you will hear people talking about 'many people', 'there were a lot of people at the concert', for example.
However it becomes slightly more complicated because sometimes you do see the word 'persons'. For example if you're in a lift or elevator you might see the sign 'Four persons only'. And sometimes if you're listening to the news, to news reports you may hear news reports talking about persons. So for example 4 persons were injured in the accident, or police are looking for 5 persons. Persons is normally a more formal use, a more formal plural form.
It gets slightly more complicated when you find the word peoples. People can be used to mean a nationality – all of the people of one country – so for example 'the people of Cuba'. And when you're talking about a group of nationalities you may find the word 'peoples', for example, 'the peoples of South America'. So that's another slightly more complicated and not so common use of the word 'peoples'.
Finally you may find the word 'person' attached to a number. For example 'a two-person car', 'a three-person room'. This is where 'person' is being used to describe the noun. '2 – person' is the adjective describing 'car' and as you know we don't put an 's' on an adjective. So far example we talk about a 'two-week holiday' not a 'two-weeks holiday' or a 'three-year course' not 'a three-years course'. So hear we use 'two-person car'.
So in summary, normally you find 'people' as the plural form of 'person' – one person, three people. Sometimes you'll find people used to describe the nationality so you'll find 'peoples' to describe different nationalities and sometimes you'll find the word 'persons' in more formal styles of writing or in signs for example.
from bbc
http://www.bbc.co.uk/worldservice/le...er/page7.shtml
