mesh currents method is circuit analysis method.
In the mesh current method, a current flowing through a resistor in a specified direction defines the polarity of the voltage across the resistor,
and that the sum of the voltages around a closed circuit must equal zero, by KVL. Once a convention is established regarding the direction of current flow around a mesh, simple application of KVL provides the desired equation.
In mesh analysis, it is important to be consistent in choosing the direction of current flow. To avoid confusion in writing the circuit equations, unknown mesh currents are defined exclusively clockwise when we are using this method