Randy,
Don't feel bad about the confusion. That is one of those questions that a lot of people have, but few people actually ask.
It's hard to follow some times because even though Bill's answer is correct, it is very common for people people to use the acronyms incorrectly.
Jeff
Some sound advice should you find yourself at the controls of an aircraft...
"Try to stay in the middle of the air. Do not go near the edges of it. The edges of the air can be recognized by the appearance of ground, buildings, sea, trees and interstellar space. It is much more difficult to fly there."
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