Carl's mother is from england and calls oregano a "herb," but his father is from the u. s. and calls it an "erb." according to your textbook, this difference in how the word sounds is a matter of

This difference in how the word sounds is a matter of "dialect".

A dialect is a type of the language that is talked in a specific piece of the nation or by a specific gathering of individuals. There are various tongues of English and they have distinctive words and grammar. It is for the most part considered that individuals who talk diverse dialects of a similar language can understand each other.