澳 is a bound morpheme (b.f.) meaning 'inlet' or 'bay', almost exclusively used in place names. You cannot use it as a standalone word — it always appears as part of a compound like 澳门 (Àomén, Macau) or 澳大利亚 (Àodàlìyà, Australia). Knowing this helps you recognize the character in geographic names and avoid trying to use it alone.