A person's "ethnicity" refers to their ethnic background, which means which group of people their ancestors belonged to.
Here are some examples of different ethnicities:
- Native American
- French Canadian
"Ethnicity" is a little different from "nationality", which is just the country that a person is from:
...and "race", which describes a few major groups of people based mostly on skin color:
The word "ethnicity" sounds kind of formal and scientific. It's usually more polite to talk about people's "ethnicity" than their "race".