An appropriate description of the substitution method would be

The substitution method is one of several methods used for solving systems of equations.  If, for example, you have a system of two linear equations in x and y, you could solve either equation for x and subst. the resulting expression in y into the other equation.  This eliminates x and allows you to find the value of y.

Example:  Solve this system of linear equations:

3x + 4y = 7
2x  +  y  = -3

Let's solve the 2nd equation for y:  y = -2x - 3.  Now substitute -2x -3 for y in the other equation:     3x + 4(-2x-3) = 3   (Note how y disappears!)

Then 3x -8x - 12 = 3; -5x = 15  => x=-3.

Again we substitute:  Subst. -3 for x in either of the given equations and solve for y.

Write your solution in the form (x,y).

These are examples of the subst. method and its applications.