Asking for explanations
I’m sorry, I’m not sure I understand.
I don’t know what you mean/that means.
What is that (exactly)?
What does HD stand for?
Can you explain …?
Could you tell me what that is/does/means?
What do you mean (by …)?
Giving explanations
It’s a/the kind/type/sort of …
It means … It stands for High Definition.
It helps you to/lets you …
