because it isn'tA conversational form of 것이 아니니까, meaning “because it is not...” or “since it isn’t...”. The word 게 is a shortened form of 것이, and the phrase usually follows a verb or adjective stem to deny an assumption or explain a reason.
KO: 걱정할 게 아니니까 편하게 생각하세요.
EN: It’s not something to worry about, so take it easy.