I would just like to add a little pet peeve...and cover it under expedience for radio etiquette.
OVER is the word you say at the end of a transmission when a reply or acknowledgement is expected. It tells the recipient that the speaker has finished talking and that the radio net is clear.
OUT is the word you say at the end of a transmission when a reply or acknowledgement is not expected or desired. It tells the recipient that the conversation is over.
OVER AND OUT is what you say to make everyone want to kick you in the nuts. You're wasting words and time on the radio, plus making it confusing for others on your team who need to use the broadcast net. They'll be like, "Is he over or is he out?" "Who cares, let's kick him in the nuts." "Good call. Then he'll be out."
Knowing the difference is the first step to being a radio god. Then you will be loved.