A compound of 高 (gāo, "high, elevated") and 兴 (xìng, "spirits, mood, interest"). The idea is that one's inner mood or vitality (兴致) is raised up (高) — a poetic image of elation that dates to Classical Chinese usage.

高兴 is the go-to everyday word for happiness in Mandarin — natural and warm across all contexts. The fixed phrase 很高兴认识你 ("very happy to meet you") is the standard polite greeting when being introduced to someone new, equivalent to "pleased to meet you" in English. Don't confuse it with 开心 (kāi xīn), which is more colloquial and often implies carefree, spontaneous joy, or 幸福 (xìngfú), which implies deep, lasting happiness or contentment (closer to "bliss" or "blessed").