The vaginal corona, also called the hymen, is folds of thin mucous tissue surrounding or partially covering the vaginal opening. All girls are born with this mucous tissue.
In most women, this tissue is quite elastic. It can be either ribbed or smooth, and it stretches over time for various reasons. The shape of the corona varies too and some people have more of it than others.
First time sex
There are people who believe that the corona ‘tears’ during first time sexual intercourse (penis in vagina) and that it creates bleeding. But this isn’t usually the case. Most girls or women don't bleed on their first time as they have quite a stretchy corona. You certainly won’t if you're turned on and relaxed when the penis enters the vagina.