Direct variation is a mathematical relationship between two variables where one variable is a constant multiple of the other. This means that as one variable increases or decreases, the other variable changes in a proportional manner. The relationship can be expressed with the equation y = k * x, where k is a non-zero constant known as the constant of variation. In direct variation, if you know the value of one variable, you can easily find the value of the other. For example, if k is 3 and x is 4, then y would be 12. This concept is commonly used in various fields, including physics and economics, to describe relationships that maintain a consistent ratio.