the action of moving away from the main subject you are writing or talking about and writing or talking about something else

Talking about money now would be a digression from the main purpose of this meeting. 现在谈论金钱将偏离这次会议的主要目的。

The book contains many interesting digressions about life in the last half-century of the regime. 这本书包含许多关于该政权最后半个世纪生活的有趣的题外话。