Digression

noun

1. 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."

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

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

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