The word lady is a term for a girl or woman, with various connotations. Once used to describe only women of a high social class or status, the equivalent of lord, now it may refer to any adult woman, as gentleman can be used for men. Informal use is sometimes euphemistic ("lady of the night" for prostitute).
"Lady" is also a formal title in the United Kingdom. "Lady" is used before the family name or peerage of a woman with a title of nobility or honorary title suo jure (in her own right), or the wife of a lord, a baronet, Scottish feudal baron, laird, or a knight, and also before the first name of the daughter of a duke, marquess, or earl.