lady ~ woman

a lady…
“Lady” (plural – ladies; for the right pronunciation, please click here) is ‘a courtesy (polite) term for a female human being’,
It is used to address:
[A]
a female human with a social rank:
e.g.
Lady Diana appeared on TV last night.
My landlady is a gentle person. [i.e. the female owner of the house or land I live in or on]
[B]
a female human in a gathering of people (only in plural) :
e.g.
The speaker said: Ladies and gentlemen! Your attention, please. [The singular ‘lady’ used for this purpose is not considered standard English; and if a singular is to be used, i.e. if there is only one female in the gathering, ‘madam’ is to be used.]
[C] a female in her presence, but not directly:
e.g.
Could you find this lady a table, please? [i.e. the headwaiter of the restaurant is asking his assistant about a female customer]
____________________

four women (gender)
“Woman” (plural – women; for the right pronunciation, please click here) is the word used for ‘a female human being to indicate sex (i.e. gender)’,
e.g.
We have two men and one woman in this picture.
He doesn’t allow his car to be driven by a woman (driver).
A woman needs more privacy than a man.
There are four women in this picture, and one of them is Lady Diana. Our queue stopped moving because a man and a Our queue stopped moving because a man and a woman before us were arguing with the cashier. [right]
Common Errors:
lady before us were arguing with the cashier. [wrong]
