「古い」 (Furui) is an i-adjective meaning 'old'. It describes something that has existed for a long time, is no longer new, or is aged. This can apply to objects, buildings, or even concepts, indicating their age or lack of newness.

「古(ふる)い」は「old」という意(い)味(み)のい形(けい)容(よう)詞(し)です。時(じ)間(かん)の経(けい)過(か)によって古(ふる)くなった物(もの)を表(あらわ)します。