Expressions are themselves objects that can return another expression when evaluated. If the expression is a simple, like a literal, then the value of the object is itself. This is called a self-evaluating expression, because it evaluates to itself. Quoted expressions also evaluate to themselves.
Symbols evaluate to the value for that name in the current environment.
I.e. a symbol is a variable name. We can write an interpreter for this language in itself. This is where EVAL comes from. Since EVAL is defined in it's own environment, we can call it ourselves. This is called reflection because the interpreter is reflected into the same environment as the rest of our code.