to move away from the main subject you are writing or talking about and to write or talk about something else

But I digress. To get back to what I was saying, this poem reflects the poet's love of nature and his religious beliefs. 我跑题了。回到我刚才说过的话上来，这首诗反映了诗人对大自然的热爱和自己的宗教信仰。

The lecturer temporarily digressed from her subject to deal with a related theory. 讲师暂时将她的主题放在一边，开始讲起了另一相关理论。

Compare: sidetrack verb