Differential

n.
  1. (Math.) An increment, usually an indefinitely small one, which is given to a variable quantity.
  2. A small difference in rates which competing railroad lines, in establishing a common tariff, allow one of their number to make, in order to get a fair share of the business. The lower rate is called a differential rate. Differentials are also sometimes granted to cities.
    1. One of two coils of conducting wire so related to one another or to a magnet or armature common to both, that one coil produces polar action contrary to that of the other.
    2. A form of conductor used for dividing and distributing the current to a series of electric lamps so as to maintain equal action in all.
    Partial differential (Math.),
    the differential of a function of two or more variables, when only one of the variables receives an increment.
    Total differential (Math.),
    the differential of a function of two or more variables, when each of the variables receives an increment. The total differential of the function is the sum of all the partial differentials.