Kenneth Fisher explains the difference between a string and an identifier:
A common mistake, and one I make frequently myself is to use a string in place of an identifier, or vise-versa. So to start, let’s have some definitions, shall we?
String
a linear sequence of characters, words, or other data.
Identifier
a sequence of characters used to identify or refer to a program or an element, such as a variable or a set of data, within it.
And because I always find examples fairly useful.
Click through for the example as well as additional explanation.