What is "acquired U.S. citizenship"?
Acquired U.S. citizenship arises when one of your parents is a U.S. citizen, either by birth or naturalization. They pass their citizenship on to you. To “acquire” U.S. citizenship, your parent must have been a U.S. citizen before you were born. It may be possible for your parents to acquire U.S. citizenship from their parents (your grandparents), and then for you to acquire U.S. citizenship from your parents.
To prove that you acquired U.S. citizenship, you must show (among other things) that your U.S. citizen parent lived in the U.S. before you were born for the required number of years. The exact requirements, including the number of years that your parent must have resided in the U.S., depend on your birth year.
If you are in removal proceedings —but think you might be a U.S. citizen—hire a lawyer or accredited representative to represent you. This article gives an overview on qualifying for relief from deportation via acquiring citizenship.