Per diem is a Latin phrase that translates to “per day.” Generally, per diem describes a daily amount paid to a person for work expenses incurred during work travel. This most commonly includes accommodation and meals, though other expenses can be included. Generally, per diem is calculated based on a set rate rather than actual expenses incurred. For example, a per diem rate might grant $20 per meal whereas a person might only spend $10. In this case, a person usually does not need to pay back the extra funds.
The federal government sets per diem each year. They vary by locality and can be viewed here. Many private companies and institutions use these rates as well.
[Last updated in July of 2020 by the Wex Definitions Team]