Meaning of the word "as hard as nails" in English

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

as hard as nails

US /æz hɑrd æz neɪlz/
UK /æz hɑːd æz neɪlz/

Idiom

very tough, unsentimental, and ruthless

Example:
She's a businesswoman who's as hard as nails when it comes to negotiations.
Despite her gentle appearance, she's as hard as nails when she needs to be.