奥 is a bound morpheme (b.f.) — it never appears alone as a standalone word, only as part of compounds. It carries the core sense of 'profound, mysterious, abstruse' in literary/formal words like 奥秘 (mystery), 奥妙 (marvelous/profound), and 深奥 (profound, of knowledge). It also serves as the abbreviation for the Olympic Games (奥运) and appears in the transliteration 奥林匹克. Additionally, it is a rare surname. Because it is bound, you never use 奥 by itself; it always attaches to another character.