By “simplifying” an algebraic expression, we mean writing it in the most compact or efficient manner, without changing the value of the expression. This mainly involves collecting like terms, which means that we add together anything that can be added together.The rule here is that only like terms can be added together.
Like (or similar) terms
Like terms are those terms which contain the same powers of same variables. They can have different coefficients, but that is the only difference.
Examples:
3x, x, and –2x are like terms.
xy^2 and x^2 y are NOT like terms, because the same variable is not raised to the same power.