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.
As stated above, the main difference between an equation and a function is that an equation usually has only one input that will give lead to the expressions being equal. Whereas, a function has various inputs, each of which will give a output.