Meaning of the word "bat an eye" in English

What does "bat an eye" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

bat an eye

US /bæt ən aɪ/
UK /bæt ən aɪ/

Idiom

to show surprise or concern; to react to something

Example:
He didn't even bat an eye when I told him I was leaving.
The news was shocking, but she didn't bat an eye.