Update concepts/type-checking/about.md

Co-authored-by: Derk-Jan Karrenbeld <[email protected]>

Author: quintuple-mallard

concepts/type-checking/about.md

@@ -12,7 +12,7 @@ For better type safety and stronger types, you should probably use TypeScript, a
 
 ## The `typeof` operator
 
-The `typeof` operator returns the type of its input.
+The `typeof` operator returns the type of its operand.
 The output is a string matching the name of one of the [primitive data types][primitives], except for `"null"`. 
 It can also be `"function"` or `"object"`.