Bean is the name used for the seeds of several plants. Most of these plants are known as legumes. Their scientific name is Fabaceae. Common beans, lentils, soybeans, Kidney beans, peas, vetches and lupins are all in that group of plants.
The seeds of other plants (which are not Fabaceae), are sometimes also called beans. This is mostly because of their resemblance to true beans. Example for such beans are Coffee beans, Cocoa beans, and Vanilla beans.