A stipend is a fixed, regular payment, usually meant to pay for something specific. It's kind of like an allowance, but for grownups — a college scholarship might include a stipend each semester for books, for example.
Coming from the Latin stipendium, which means “tax, pay, or gift,” the noun stipend is defined as a regular, unchanging payment usually given as reward for services, but sometimes given as an allowance with no services or expectations attached. A summer internship that does not offer a full salary might instead include a weekly stipend that covers transportation and lunch costs. Synonyms include salary and payment.