Algebra is that branch of mathematics which treats the relation of numbers. In algebra, two types of symbols are used: constants and variable (literals).
What is a Constant :
It is a symbol whose value always remains the same, whatever the situation be. For example: 5, –9, 5/2 , π, , etc.
What is a Variable : It is a symbol whose value changes according to the situation. For example : x, y, z, ax, a + x, 5y, – 7x, etc.