Why are bank holidays called "bank holidays"?

Bank holidays originally referred to the official holidays in the United Kingdom Bank Holiday Act of 1871. This act has changed over the years, but it still remains the origin of the name.

There is nothing in the Bank Holiday Act that says it is mandatory for employers to give these days off to their employees or to pay them for time not worked if they do give them the day off. As of 2014, it is more of a suggestion and a guideline for when to offer days off to employees so they can enjoy time with their families.