The word lady is a polite term for a woman, specifically the female equivalent to, or spouse of, a lord or gentleman, and in many contexts a term for any adult woman. Once relating specifically to women of high social class or status, over the last 300 years it has spread to embrace all adult women, though in some contexts may still be used to evoke a concept of "lady-like" standards of behaviour.

The word comes from Old English hlǣfdige; the first part of the word is a mutated form of hlāf, "loaf, bread", also seen in the corresponding hlāford, "lord". The second part is usually taken to be from the root dig-, "to knead", seen also in dough; the sense development from bread-kneader, or bread-maker, or bread-shaper, to the ordinary meaning, though not clearly to be traced historically, may be illustrated by that of "lord".

The primary meaning of "mistress of a household" is now mostly obsolete, save for the term landlady and in set phrases such as "the lady of the house." This meaning is retained in the southern states of the USA, however, in the title First Lady for the wife of an elected official. In many European languages the equivalent term serves as a general form of address equivalent to the English Missus usually written Mrs (French Madame, Spanish Señora, Italian Signora, German Frau, Polish Pani, etc.). In those languages it is correct to address a woman whose name is unknown as Madame, Señora, etc., but in English "lady" has for centuries only normally been a "term of address" in the plural, which is also the case for "gentleman". The singular vocative use was once common but became confined to poetry. The equivalent English term for politely addressing a woman is Madam or Ma'am.