节日 (jiérì) refers to a specific festival or celebration, like the Mid-Autumn Festival or Christmas — a cultural or traditional event. 假期 (jiàqī) and 假日 (jiàrì) mean 'vacation' or 'day off,' focusing on time off rather than the celebration itself. 节 (jié) is the shortened form used in festival names (春节) but can also stand alone as 'festival,' though 节日 is more common as a standalone word.