LHS means left hand side

RHS means right hand side

These are used in the equation.

Example: 

               x-2 = 7

In this equation

LHS is x-2 and RHS is 7

While solving such type of equation, we always put variable on LHS and non-variable on RHS 

In the above example given that

      x-2 = 7

=> x = 7+2  (take -2 and put it on RHs, so it becomes +2)

=> x =9