The symbol "\partial y" represents a partial derivative with respect to the variable y. In calculus, a partial derivative measures how a function changes as one variable changes while keeping other variables constant. This is particularly useful in functions of multiple variables, where understanding the effect of one specific variable is essential. For example, in a function f(x, y), the partial derivative \partial y indicates how f changes when y varies, while x remains fixed. This concept is fundamental in fields like physics, engineering, and economics, where systems often depend on several interrelated variables.