“She was really sharp.”
You're interviewing for new employees at the store you manage. You're reviewing the list of applicants with a coworker. You comment on the next person on the list, who seemed smart.
She was really sharp.
A "sharp" person is smart. They notice important details and make good decisions quickly.
Anita? Yeah, she's great to work with. She's so sharp!
Compared to other words like "smart" and "intelligent", "sharp" sounds a little more quick and active. An "intelligent" person might read a lot or be able to solve complicated problems, but a "sharp" person is smart in a very practical way.