The word simplify means make simpler. To simplify an expression
is to remove unnecessary numbers or terms, usually by cancelling
or factorising. This may apply to working out a numerical
problem or grouping together like terms in an algebraic expression
in most concise way.

For example, 3p^{3}q x 2pqr = 6p^{4}q^{2}r

2(x + 3y) + 3(4x - y) = 2x + 6y + 12x - 3y = 14 x + 3y