Hello everyone.

What does yet mean and what type of word it is here?

Although he has yet to expand on what that means.

I don’t think it’s a complete sentence.

“he has yet to expand on something” means “He hasn’t expanded on something yet and he is going to expand on it”.

It’s an adverb meaning ‘up to the present time, up to now’.
We can’t say that ‘he is going to expand on it’.

The sentence:
[color=indigo]In time, he may yet expand on this.
Here, the ‘may yet’ indicates that the speaker thinks that may happen in the future.

has yet to do means something hasn’t done yet.

I think it depends on the situation where we use the sentence.

You are right. That sentence can be used.