The document discusses linear systems of equations and their properties. It defines a linear system as a collection of linear equations involving the same variables. A linear system can have either no solution, exactly one solution, or infinitely many solutions. A system is considered consistent if it has one solution or infinitely many solutions, and inconsistent if it has no solution. The document provides examples of consistent and inconsistent systems, and shows how to use row reduction to determine if a system is consistent or inconsistent.