Does ribit only apply to loans? If not what else does it apply to? thanks
You are asking an important question. Yes, ribit does not only apply to monetary loans, it applies in numerous other places, such as when selling an item for a cheaper price if the money is given up front, when food is given and it will be returned at a later date, or in a business partnership when one person gives the money and the other does the work. It would even apply when one person buys something on another persons credit card and it accrues interest. The halachos of ribit can come up more often than most people think, and they are complex and need studying. I would recommend that you see a sefer written by R’ Y. Reisman shlit”a called “The Laws of Ribbis” to read and familiarize yourself with these halachos, and also as a source of reference when a question comes up.