Terms
Triangular System: n equations and n variables, like this example where n=3
Echelon System: A system of m linear equations in n variables is called an echelon system if. m ≤ n. Every variable is the leading variable of at most one equation. Every leading variable is to the left of the leading variables of all lower equations.
Back Substitution: The intuitive method of solving a triangular system, going from the bottom to the top so that the equation with one variable is solved first.