Which of the following terms is used to express ideas related to a particular trade?

a. "colloquialism."

b. "idiom."

c. "jargon."

d. "slang."

Jargon is a term used to express ideas related to a particular trade.

Explanation:

Let's define each term:

Colloquialism- the use of ordinary words or phrases

Idiom- a group of words that do not have a literal meaning, but the meaning is understood (example: it's raining cat's and dogs)

Jargon- Words that are used in a particular profession and are difficult for others to understand (legal jargon, medical jargon)

Slang- very informal words

Based on these definitions, it is easy to see that jargon is the term used to express ideas related to a particular trade, like law or medicine.