厚此薄彼 is a four-character idiom meaning 'to show favoritism'—literally, 'to treat this one thickly (i.e., generously or warmly) and that one thinly (i.e., coldly or dismissively).'

The idiom contrasts two sides: 厚 (hòu) means 'thick', used metaphorically for warmth, generosity, or strong support; 薄 (bó) means 'thin', implying neglect, indifference, or unfair slight. 此 ('this') and 彼 ('that') refer to two distinct people, groups, or things being compared. It’s commonly used in formal or critical contexts—such as education, management, journalism, or social commentary—to condemn biased treatment, especially when fairness is expected. While it can describe personal bias, it most often appears in discussions of institutional or systemic inequity.