That is not an idiom. It means just what it says. You need a medical dictionary to look up medical conditions, not an idiom dictionary.
I think by idiom, you may be asking what type of language is represented by the phrase "inflammation of nictitating membrane." That phrase is typical of medical or scientific terminology rather than common or lay language.
"To be" is not an idiom - it's a verb.
The idiom "apple shiner" means the teacher's pet.
It is actually an idiom.
My Favorite IDIOM Is, When Pigs Fly.
Pest is not an idiom. It's a word.
The nictitating membrane is the transparent layer the covers the outside of a frogs eye. Frogs have a so-called Nictitating membrane, which they can slide over their eyes for protection. They do this while jumping and swimming.
The membrane is. SOME problems with it are too.
The nictitating membrane.
depends on the species.
A nictitating membrane The nictitating membrane is the THIRD eyelid, the SECOND eyelid that you asked about is just that, the eyelid, just like in humans
The nictitating membrane is part of a frog's eye. It is just above the lower lid and acts as a protective third eyelid.
Nictitating membrane
nictitating membrane is cartilage.
Nictitating Membrane
nictitating membrane
depends on the species.
It's called the Nictitating membrane