How to address a woman?

1. Note that do not address anyone with their first name unless they are well know to you or they are your friends.

e.g. Mrs. Michelle Obama
Here 'Michelle' is the first name. And 'Obama' is the surname of Michelle's spouse(husband).

You could address her as Mrs. Michelle or Mrs. Obama or Mrs. Michelle Obama.

2. If you are not sure about the marital status of a woman over 30yrs of age you should use 'Ms.'

e.g. Ms. Aishwarya Rai
When using 'Ms.' the surname could either be the surname prior to her marriage or her partner's surname if she is married.

3. And 'Miss' is used for girls and women under the age of 30.

e.g. Miss Amy Alba

What is maiden name?
Maiden name is the surname of a girl or woman before her marriage.

What is pet name?
Pet name is the name by which she is affectionately called by people who are close to her.

e.g. 'Miss Katrina' could be called as 'Kat' by her close friends.