What is Business Day?

Legal Definition
A business day is considered every official working day of the week. Another common term is working day. Typically, these are the days between and including Monday to Friday and do not include public holidays and weekends.

The definition of a business day varies by region. It depends on the local workweek which is dictated by local customs, religions, and business operations. For example, in the United States and much of the Western world, they are typically Monday to Friday. Within the European Union, the normal business days are Monday to Friday based on the working time regulation of the EU.

Business days are commonly used by couriers when determining the arrival date of a package. If a courier ships a parcel on a Thursday that will be delivered in "two business days", it will arrive on the following Monday if neither Friday nor Monday are a holiday.

In finance, how business days are defined are called "business day conventions" and determine how payments are settled on contracts such as interest rate swaps.
-- Wikipedia
Legal Definition
A business day is considered every official working day of the week. Another common term is working day. Typically, these are the days between and including Monday to Friday and do not include public holidays and weekends.