It includes the basic elements of getting your message out as well as barriers to communicating effectively. Effective communications involves each of these interrelated elements and if only one gets mixed up, communication doesn't happen. Let's take an example. Not very likely. Suppose you, having done everything properly, make your call but get no response.
Communications happen when someone sends ideas or thoughts to another person or group of people.
One measure of how well this someone has communicated is by how similar the received information is to that which was sent. Think back to when you were a student pilot. Maybe your CFI said to watch out for a certain airplane when performing stalls as one wing was likely to fall off if you were not coordinated when the stall occurred. And so on. The Aviation Instructors Handbook lists three.