Dear student,
Entropy is the measure of degree of disorder or randomness. It is denoted by symbol S.
For e.g. a gas is more random than liquid which in turn is more random than solid. Thus entropy follows the order:
Gas>liquid>solid
When a system undergoes a change from one state to other state, change in entropy takes place which is denoted by symbol ΔS, where
ΔS=q/T
Regards