To "Digress" is to stray from the main subject.
Digress is a verb.
Synonyms: turn aside, wander, deviate.
Antonyms: continue, proceed, advance.
In forum threads of ISC if a person digresses from the main topic then he will be credited with negative points.
Sometimes it is wise to digress for a moment in a long speech and tell a joke just to keep the attention of the people.
Mr.Ravi digressed so often that we could not remember the original topic.