What is a vitreous?

a clear gel in the eye that fills the space between the lens and the retina in your eyeball.

The vitreous cavity also known as the Vitreous Humor is A jellylike transparent fluid fills the inner chamber of the eye. This fluid is called the vitreous humour and it is contained in a thin...

posterior vitreous detachment is a condition of the eye in which the vitreous humour separates from the retina

The "Vitreous Jelly" or what you may mean, the vitreous humor, is clear gel (which I assume can be likened to glass), that is between the retina and lens of the human eye.

this fills the space between the lens and the retina in your eyeball