Hi,

If “Do you copy?” means “Do you hear me?”, can we say, “I copy” to mean “I understand”? Yes, although this is mainly for talking over two-way radio, eg in a police-car.. 

1. Does “I didn’t catch your name” mean “I couldn’t hear your name” or “I don’t remember your name”? Both.
2. What does “Do you read me?” mean? More lor less the same as 'do you hear me'. 'Do you understand me'?
3. What is the difference between “What do you mean?” and “How do you mean?” In simple terms, 'what' refers to the subject you are discussing, but 'how' refers to the method of doing what you are discussing. However, sometimes people use these terms less carefully.
4. What is the pronunciation of ID? eye dee Is “ident” a variant short form for it? Not in speech, although you might sometimes see it in writing (followed by a period).

Best wishes, Clive

Hello, Indefatigable, and welcome to the forums!

Permit me to disagree with you, in turn, on your #2 above.  Your use of "I didn't catch your name" is a great, polite way to handle a situation if you never did learn the name in the first place.

But if you're at a party and someone says "Oh, hi. Do you know Sue, Pete, [mumble], and Sarah?" It's perfectly natural to say to the third person, "I'm sorry, I didn't catch your name?"

Also, on #3: I know that I have heard people say things like "So, if I'm reading you correctly, what you really want is..." to mean "If I properly understand you."  It doesn't refer to literally hearing them, but understanding their meaning.  And people will say "I couldn't get a read on him today" which means "I couldn't get a good sense of his mood" or "I couldn't really tell what he was hoping to achieve from that meeting."