Travel and subsistence expenses describe the cost of spending on business travel, meals, hotels, sundry items such as laundry (though usually only on long trips) and similar ad hoc expenditures.
An organisation may refund or reimburse these costs on the basis of an itemised list, or may conclude that cost of doing so is disproportionately high and instead pay a per diem (per day, "day money") allowance. This provides a budget from which the traveller may recover their costs. In this case, the traveller may choose to stay in more expensive hotels (for example) and pay the additional cost themselves.