徇私 is a separable verb (离合词) meaning 'to act in someone's interest out of personal favoritism, usually to violate rules or fairness'. The verb 徇 ('to comply with') splits from the object 私 ('private/personal') when inserting other elements: 徇过私 ('have shown favoritism'), 徇了私 ('showed favoritism'). It's often used in formal or critical contexts, such as accusations of nepotism or corruption.