Meaning of the word "as keen as mustard" in English

What does "as keen as mustard" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

as keen as mustard

US /æz kiːn æz ˈmʌstərd/
UK /æz kiːn æz ˈmʌstəd/

Idiom

very enthusiastic and eager

Example:
She's always as keen as mustard to learn new things.
The new recruits were as keen as mustard on their first day.