The Nation of Islam is a nationalistic movement that began in the early 20th century, whereas Islam is a religion that was revealed in the 7th century.
The original Nation of Islam was a hierarchical organization. However, In 1975 Elijah Muhammed's son W.D. Muhammed disbanded the organization and moved his followers towards traditional Islam.
The Nation of Islam was revived within a few years by various individuals, with the organization headed by Louis Farrakhan being the most prominent of these. Today, followers of his organization number less than 100,000 people, compared with the majority of African Americans who follow Islam. Unlike today's Nation of Islam members, most mainstream Muslims are not part of a hierarchical organization.
In terms of ideology the Nation of Islam differs in two major ways: the founder of the movement, W.D. Fard, is considered God incarnate and Elijah Muhammed is considered a prophet by members of the Nation of Islam. While there are other differences between the two, the Nation has adopted many Islamic traditions, such as women's dress, holidays and some Islamic terms.