What english term descibes a noun?

the answer:

in the first part of the story running is all that matters to squeaky. running gives her confidence and defines who she is. at the beginning of the story she says that other kids call her mercury because she runs very fast. in the text she refers to herself as "miss quicksilver".

the line that provides the best evidence that squeaky has self-confidence is

" and i continue with my breathing exercise, strolling down broadway toward the ice cream man on 145th with not a care in the world cause i am miss quicksilver herself".