The Word Outsider In S. E. Hinton's 'The Outsiders'

When S.E Hinton adopted the title ‘The Outsiders’ for her book even though the word “outsider” was never recorded in the book itself making it the title was an intelligent move on her part. However, an outsider, in my opinion, is someone who doesn’t follow the flow that everyone else follows. For instance, many things could make you an outsider, including your appearance, your family, the way you live, and how you perform with other people. But why was it so critical for Hinton to use the word “outsider” when she could’ve used “greasers” or “socs”? Perhaps, Hinton preferred to use the word “outsider” because of the greaser characters in the books. The greasers weren’t rich, they didn’t have the right clothes or wore their hair the right way.