The term "factor of proportionality" refers to a mathematical constant that helps to establish a relationship between two quantities. This constant can also be referred to as a proportionality factor, a scaling factor, or a ratio. When two quantities are directly proportional, the factor of proportionality is the ratio between them. Other synonyms for this term include a proportionality constant, a conversion factor, or a unit rate. Essentially, this factor helps to determine how much one quantity changes in relation to another. It is a crucial concept in fields such as physics, economics, and mathematics, where understanding proportional relationships is essential.