A toll-free number is a special phone number in which the cost of the call is transferred to the owner of the number. The business pays to receive their customers calls making the call effectively free for the caller.
These kind of numbers are also called 800 numbers, because they are often in the range of 800 to 899, like in +1 800 123 4567, +1 844, 123 4567, +1 888 123 4567, 01 800 111 222, etc.
You can easily get toll-free phone numbers in USA, Canada, Australia, UK, Brazil, México and other countries.