Assimilation refers to the pattern by which:

Assimilation refers to the pattern by which minorities gradually adopt patterns of the dominant category.

For example, if you live in America, and you suddenly decided that you wanted to move to Japan, in Japan you would be a minority, given that 97% of people living in Japan are Japanese. However, over time, after living in Japan for years, you would become assimilated to their culture, and accept it as your own.