Difference between suburb and suburbs?

[Rei]

Hi, from Japan! :-)
Could anyone tell me what the difference between suburb and suburbs is?

I've seen sentences like "I live in the suburbs of New York."
and "an agricultural suburb".

When do you use suburb and when suburbs?

Thanks!

[Mister Micawber]

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One suburb, two suburbs.
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Native English teacher at Mister Micawber's

[Yankee]