背地里 is an adverbial phrase meaning 'behind someone's back' or 'privately'. It describes actions done when the person involved is not present or unaware, often with a connotation of secrecy or gossip. You can use it with verbs like 说 (to speak), 做 (to do), or 讨论 (to discuss) to indicate something is done without the target's knowledge. Note that the input pinyin for 背 is given as bēi, but in standard pronunciation for this phrase, 背 is read as bèi (4th tone); the original data's tone marking may be incorrect.