digression

noun

• An aside, an act of straying from the main subject in speech or writing.

  "The lectures included lengthy digressions on topics ranging from the professor's dog to the meaning of life."

• The act of straying from the main subject in speech or writing, particularly for rhetorical effect.

  "make digression... by way of digression..."

• A deviancy, a sin or error, an act of straying from the path of righteousness or a general rule.
• A deviation, an act of straying from a path.
• An elongation, a deflection or deviation from a mean position or expected path.