What does "tough cookie" mean?

A person who can endure physical or mental hardship; a hardened, strong-willed person.

Tough cookie

noun, slang

noun, slang ·Moderate ·College level

Noun

1
A person who can endure physical or mental hardship; a hardened, strong-willed person. informal
"An austere, hard-lining rightist, who lives alone, Ioannidis is described by one Washington military official as "a real tough cookie.""
2
A hardy, resilient animal or plant. informal
"Boxwood is a pretty tough cookie. Wind, cold, wet, exhaust fumes, and industrial pollution are of no consequence."
3
Something troublesome or difficult to handle. informal
"The pup that struggles constantly might be one tough cookie when it comes to training; […]"

"An austere, hard-lining rightist, who lives alone, Ioannidis is described by one Washington military official as "a real tough cookie.""