Double hyphen

A double hyphen is when you write two hyphens next to each other like this "--". It's used in writing to show that you're adding some extra information or a modifying phrase to a sentence. It's kind of like a pair of parentheses, but instead of using curved lines, you're using straight lines.

For example, let's say you're writing a sentence about your friend John, but you want to add some extra details about him. You could write, "My friend John--who loves to play video games--is coming over to my house." The double hyphens show that the phrase "who loves to play video games" is extra information about John, but it's not necessary for the sentence to make sense.

So, the idea behind a double hyphen is to signal to the reader that the information within the hyphens is additional or somewhat aside of the main sentence's idea, but still contributes to it.