The conjunctiva is the clear, thin tissue that lines the inside of your eyelid and covers the white of your eye.
Sub means under, and hemorrhage means bleeding. So a subconjunctival hemorrhage is a small collection of blood underneath the conjunctiva. The whole white part of your eye or just some of it will be bright red.
The blood comes from a small broken blood vessel on the surface of your eye
A subconjunctival hemorrhage doesn't affect your vision
A subconjunctival hemorrhage may look scary but is harmless unless whatever caused it also damaged other parts of your eye
It goes away on its own, usually within 2 weeks