光临 (guāng lín) is a formal, polite verb meaning 'to honor with one's presence' — used when inviting or welcoming someone to a place or event. It is more courteous than 出席 (chū xí, simply 'to attend a meeting/event'), and unlike 光顾 (guāng gù, 'to patronize a store'), it is not limited to commercial settings. 莅临 (lì lín) is even more elevated, reserved for very distinguished guests.