유행어가 · 유행어를
buzzword, catchphrase, popular expression
Example
그 개그맨의 말은 금세 유행어가 되었어요.
That comedian's line quickly became a catchphrase.
Word parts
유 flow+행 go+어 word
Literally 'word that is in fashion'; -어 = word or language: 신조어, 외래어.
Good to know
유행어 is a catchy phrase that's popular now; 신조어 is a newly coined word.
Related words