800 number

Etymology
In the original North American Numbering Plan, phone numbers beginning with an area code of "800" were reserved for so called toll-free numbers, where the party receiving the call pays the charges. As more toll-free numbers were needed, additional area codes were added to the scheme including 888, 877, 866, 855, 844, 833 and one more was reserved: 822. The term "800 number" is used colloquially to refer to all of these.

Noun

 * 1)  A toll-free telephone number.