In modern society, use of the word lady to refer to an adult human female is a complex business. Originally a term restricted to a woman of superior social position, such as feudal superiority, birthright or as a woman of particular refinement, education of accomplishment, by the beginning of the 20th Century the word “lady” was used habitually as a courteous reference to every respectable woman. Although upper class women did not seem to mind being referred to as “women”, and indeed sometimes indicated a preference for it , middle and lower-class women insisted on being referred to as “ladies”.
By the end of the 20th Century, new sensitivities had emerged, and the issue of sexism in language again revived questions on the appropriate use of the word “lady”.
Today “women” is generally considered the appropriate term in academic and social circles, except in such entrenched phrases as “Ladies and Gentlemen” and “lady of the house”.
Lady is a rank, form or address, or courtesy title in several levels of the British aristocracy. The general rule is that is mirrors the use of “Lord”.