Simple Definition:

Ethnicity is a term that refers to a person’s cultural background or heritage [where they come from and their traditions]. It is based on factors such as nationality, race, language, religion, and customs. For example, someone might identify as being of Hispanic ethnicity if their family is from a Spanish-speaking country like Mexico or Colombia.

Very Simple Definition:

Ethnicity means where someone’s family comes from and what traditions they have. For example, if someone’s family is from Mexico and they celebrate Mexican holidays, they might say their ethnicity is Mexican.