Digression (noun)

1. A departure from the main subject or the straight path; a straying from the point.
2. A section of speech or writing that is not directly related to the main topic.

Origin:

From the verb digress, meaning "to depart from a subject".

Examples:

1. The digression was not relevant to the discussion.
2. His digressions made it hard to follow his train of thought.
3. The conversation included several digressions before returning to the main topic.
4. The digression in the novel was a tangent that was not necessary for the story.
5. The digression was a brief departure from the main topic before returning to it.