What is the difference between toll-free number and 800 number?

An 800 number is a toll-free number. Originally, all toll-free numbers used the 800 area code. So everyone knew that dialing 800 was toll-free and "800 number" became the commonly used phrase (vs. "toll-free"). After all the 800 numbers were used, and new toll-free area codes had to be issued, it was not obvious that these non-800 phone numbers were toll-free. Therefore, a toll-free number that does not begin with 800 is usually specified as "toll-free" so the caller knows there is no charge for the call. The toll-free codes in North America are 800, 888, 877, 866, 855, and 844, with 833 and 822 reserved for future toll-free use.

Bottom line: in North America (USA, Canada, etc.), all 800 numbers are toll-free numbers, but not all toll-free numbers are 800 numbers.