Integration is a term that has two meanings:
Providing stability to a social group: Without a certain level of integration, social organisation cannot exist. In this sense, integration includes organisational principles like the division of labour, the public celebration of solidarity, norms and rules, etc.
Acculturation, i.e. the process of making someone equal or fitting to the rest of society. The concrete measures to produce integration of immigrants can vary according to the concept of culture that is being used. Nearly all concepts of acculturation, though, implicitly assume, that 'native' members of a host country already share the same traits which the immigrants still have to attain. Acculturation inevitably aims at reducing cultural diversity.