skillfulness by virtue of possessing special knowledge
"Her expertise in ancient cryptography allowed her to decode the mysterious message that had stumped experts for years."
Great skill or knowledge in a particular field or hobby.
"After years of restoring vintage watches, she gained expertise that allowed her to fix pieces others thought were beyond repair."
In plain English: Expertise is the high level of skill and knowledge someone has in a specific area.
"Her expertise in computer programming helped her team solve the difficult bug quickly."
Usage: Use expertise to describe a high level of skill or deep knowledge that someone possesses in a specific area. It functions as a singular noun indicating the quality of being an expert rather than referring to the act of showing off one's abilities.
The word entered English directly from French as expertise. It retained its original meaning of specialized knowledge or skill without significant change.