Word for off-topic discussion

I need a word that simply means "off-topic discussion." Banter is close because it means playful remarks, which can possibly denote off-topic discussion, but not really. Is there a word for this?

"We need to stay focused on the topic at hand and avoid all of this _____."

Solution 1:

"Tangent" is the word that comes to mind, although it doesn't fit into the blank you've left.

E.G.

"During the lecture on the civil war, Ms. Appleby went off on a tangent and told us all about the time her dad fell down the stairs."

"Although our discussion of peach farming was tangent to the given topic of crop rotation, it was still fruitful."