节日(jié rì) - festival, celebration in Mandarin

节日 (jiérì) is the general word for "festival" or "holiday": 节 (jié) means "festival, occasion" and 日 (rì) means "day". It is the umbrella term that covers every named celebration, from 春节 (Chūnjié), Chinese New Year, to 中秋节 (Zhōngqiūjié), the Mid-Autumn Festival, to foreign ones like 圣诞节 (Shèngdànjié), Christmas.

Notice that most specific festival names end in 节 (jié) for exactly this reason: 春节 (Chūnjié), 中秋节 (Zhōngqiūjié) and 端午节 (Duānwǔjié), the Dragon Boat Festival, are all built on the same character that gives 节日 (jiérì) its meaning.

Use 节日 (jiérì) when speaking generally, as in 你最喜欢的节日是什么？(Nǐ zuì xǐhuan de jiérì shì shénme?), "what's your favourite festival?", and switch to the specific name once you know which one you mean.