The constant of variation is a ratio that represents the relationship between two variables that are directly proportional or inversely proportional to one another. In a direct variation, the constant of variation is the constant ratio of two variable quantities, and it is denoted by k. The formula for direct variation is y = kx, where y and x are the two variable quantities, and k is the constant of variation. In an indirect variation, the constant of variation is the constant product between two variable quantities, and it is also denoted by k. The formula for indirect variation is y = k/x, where y and x are the two variable quantities, and k is the constant of variation. The constant of variation is also known as the constant of proportionality or the constant of variant.