If a phone number is toll-free, you pay nothing to call it. The company you are calling pays instead. This is the normal American word; in Britain people usually say freephone, and a British freephone number starts with 0800. Toll-free works as an adjective — a toll-free number, a toll-free hotline — and also as an adverb: 'Call us toll-free on 1-800…'. In the US these numbers begin 1-800, and also 888, 877, 866, so American people often just say 'an 800 number' and mean the same thing. You mostly meet the word in advertising, on packaging, and at the end of TV commercials — it is a selling point, a small promise that asking costs you nothing. Note that toll-free says nothing about the service being free; you may still be told to pay for the product. Only the call is free. The word toll on its own means money you pay to use a road or bridge, and that older sense survives in toll road and tollbooth — so toll-free literally means 'no fee to pass through'. In practice the phone sense is what you will hear ninety-nine times out of a hundred. One small thing: calling a US toll-free number from another country usually does not work, or is not free, because the company only pays for calls inside its own country.