Meaning of the word "holy grail" in English

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

holy grail

US /ˌhoʊ.li ˈɡreɪl/
UK /ˌhəʊ.li ˈɡreɪl/

Noun

something that is extremely difficult to find or achieve

Example:
Finding a cure for cancer is often referred to as the holy grail of medicine.
For many scientists, discovering extraterrestrial life is the ultimate holy grail.