What type of loan primarily involves only interest payments?

The type of loan that primarily involves only interest payments is known as a straight loan. In a straight loan, borrowers make interest payments on the principal amount for a specified period, and at the end of that period, the full principal amount is due. This structure allows borrowers to maintain lower monthly payments during the term of the loan since they are not paying down the principal initially.

Other loan types, like conforming loans and Federal Housing Administration (FHA) loans, include typical amortized structures where both principal and interest are paid over the life of the loan, resulting in higher monthly payments compared to a straight loan. A package loan, on the other hand, is a type of financing that includes both real estate and personal property but does not primarily focus on interest payments only. Thus, a straight loan uniquely serves this purpose, making it the correct answer.