The phrase “coined the term” is used to mean that someone basically created a commonly used term, so “coined the term” is synonymous with “created the phrase” or “was the first to use the phrase”.

What does coined the term mean?

to invent a new word or expression, or to use one in a particular way for the first time: Allen Ginsberg coined the term "flower power". SMART Vocabulary: related words and phrases.

Why do we say coined the term?

"It takes all sorts to make a world, to coin a phrase." ... This usage derived from an earlier 14th century meaning of coin, which meant wedge. The wedge-shaped dies which were used to stamp the blanks were called coins and the metal blanks and the subsequent 'coined' money took their name from them.