Merge pull request #3569 from agoziemax/patch-1

Update part9a.md

Author: mluukkai

src/content/9/en/part9a.md

@@ -52,6 +52,11 @@ const age = 22;
 console.log(birthdayGreeter(birthdayHero, age));
 ```
 
+#### Keywords
+
+Keywords in TypeScript are specially reserved words that embody designated teleological meaning within the construct of the language. They cannot be used as identifiers (variable names, function names, class names, etc.) because they are part of the syntax of the language. An attempt to use these keywords will result in syntax or semantics error. There are about 40-50 keywords in TypeScript. Some of these keywords include: type, enum, interface, void, null, instanceof etc.
+One thing to note is that, TypeScript inherits all the reserved keywords from JavaScript, plus it adds a few of its own type-related keywords like interface, type, enum, etc.
+
 #### Structural typing
 
 TypeScript is a structurally typed language. In structural typing, two elements are considered to be compatible with one another if, for each feature within the type of the first element, a corresponding and identical feature exists within the type of the second element. Two types are considered to be identical if they are compatible with each other.