信佛 means 'to believe in Buddhism' or 'to be a Buddhist'. It is a verb-object compound (离合词): 信 ('believe') + 佛 ('Buddha'). You can insert aspect markers or measure words between the two characters, e.g., 信了佛 ('became a Buddhist'), 信过佛 ('have believed in Buddhism'). The term implies not just intellectual belief but also religious practice, devotion, and following Buddhist teachings. It is culturally loaded—being a Buddhist in Chinese society often involves temple visits, vegetarianism, and moral precepts.