What does a sea of glass mean in revelations chapter 4 verse 6?

Answer 1

The phrase "a sea of" often means "a wide expanse of"

- "there was a sea of people in the streets when the procession was passing"

- "the prairie resembled a sea of grass, moving gently in the breeze"

- "the venue was littered with a sea of rubbish after the concert."

So, a wide area of glass. Probably referring to a very highly polished floor made of some type of stone.

--- another answer ---

When the earth was made it was made like a sea of glass.

It is the earth, in its sanctified, immortal, and eternal state