Final answer:
Per Diem is best described as 'Within a day' and refers to a daily allowance for expenses incurred, often used when employees travel for business.
Step-by-step explanation:
The term Per Diem is best described as d. Within a day. The phrase 'per diem' originates from Latin and literally means 'for each day'. In professional or business contexts, it often refers to the allowance or reimbursement for daily expenses, such as meals and lodging, when traveling for work. This is separate from salary or hourly wages and is meant to cover the cost of living away from home temporarily. For example, an employee on a business trip may receive a per diem to cover their costs without having to submit a detailed expense report.