庆 is a bound morpheme (cannot stand alone as a word) meaning 'to celebrate' or 'celebration'. It appears in common compounds like 庆祝 (to celebrate), 国庆 (National Day), 庆典 (celebration ceremony), and 庆贺 (to congratulate). It is also a surname. When used as a verb or noun, it must be combined with another character; it is not used independently.