A string is a collection of characters whereas a symbol is a static identifier. A string is not static no matter what the contents of the string are. So the strings "hello" and "hello" are two different objects, whereas the symbol :hello and :hello are the exact same object. If you think of 1 as a FixNum or fixed number, you can think of the symbol :hello as the "FixStr" or fixed string :hello.

Your answer is close- in that symbols are identifiers, but they can identify anything, not just strings.