Loanword from English; used to describe someone who works diligently and puts in a lot of effort. Often carries a positive or admiring tone.
He is a real hard worker, staying late every day.
The hard-working employees led the project to success.
Variant with interpunct, sometimes used for clarity or emphasis.
Borrowed from English 'hard worker'. The exact date of borrowing is uncertain, but it became common in Japanese business contexts in the late 20th century.