What is race?
From what I have learned in school race is just a simple way to describe certain groups of people from distinct areas that are in certain parts of the world, but with the amount of migration that we have all over the world it would be more difficult to use this definition to describe what race means.
What is ethnicity?
I have never had a good understanding of what ethnicity means or I haven't been able to define it in my own words. I would have to say ethnicity would just be a group of people that have common traits and are distinguished by those traits to be of a certain ethnic group.'
What is Nationality?
This might be the simplest of all three to understand. Nationality just refers to the country that you have gained citizenship in. I have seen a lot of people ask others what their nationality is, when what they are trying to ask is what their ethnicity is.
How are they similar/different?
Some similarities with these three words are that when these words are used to describe someone it can cause confusion amongst each other since not everyone has a clear understanding of what these words actually mean or some people don't know what the word means at all.