姬 (jī) is a bound form (b.f.) used in classical and literary Chinese, typically appearing in compound words. It can refer to an imperial concubine or a woman (often in historical or artistic contexts, e.g. 歌姬 'female singer-entertainer', 舞姬 'female dancer'), or it can be a surname. You will rarely see 姬 used alone as a standalone word in modern Mandarin; instead, it is part of set compounds or historical names.