Definition of dray. : a vehicle used to haul goods; especially : a strong cart or wagon without sides.
The main difference between an equation and a function is the fact that an equation usually deals with a single input, whereas, a function can have numerous inputs. In mathematics, an equation is used to denote the equality between two expressions.
expression, formula. a group of symbols that make a mathematical statement. the equation representing the relation between selected values of one variable (x) and observed values of the other (y); it permits the prediction of the most probable values of y.