Before we discuss the closed-loop gain, let’s review a concept: transfer function. A transfer function is a mathematical representation of the relation between the input and output of a system.
The transfer function of a closed-loop configuration is G=A/(1+βA), which is the closed-loop gain. Where A is open loop gain, β is feedback factor, βA is loop gain. It is easy to see the difference between closed loop gain and open loop gain.