So, ethnic group is not a mere aggregate of people or a sector of population, but a self-conscious collection of people united, or closely related, by shared experiences.
The Cambridge dictionary defines ‘Ethnic’ as – a large group of people who have the same national, racial, or cultural origins, or the state of belonging to such a group
An Ethnic Group is usually bigger (in numbers) than a tribe (though the terms can overlap, as in the example of Kenya or other large African communities. It comes from the Greek word “Ethnos”, which can also be translated as “Nation”, and is similar to the Latin “GENS” from which the English word “Gentile” comes (that is used in English to translate the Hebrew “goy”, which means “nation”). An “ethnic group” is usually one with a shared language and culture, and whose members have enough in common to perceive themselves as a distinct group.
In India, the word “ethnic” is often replaced by “tribe”. But it can be lamely quoted as tribe is more like a lifestyle. They are characterized by their relatively small size compared to the population of a town. Tribes also have the tendency to be traditional, in terms of lifestyle and technology.
On the other hand, ethnic groups aren’t just exclusive to tribes. They can be people who live in modern big city who share some common similarities.
A nation can consist of multiple tribes/ethnic groups. They are usually associated with a country, but also a territory that is relatively large enough.