Kotlin keywords are predefined, reserved words used in Kotlin programming that have special meanings to the compiler. These words cannot be used as an identifier (variables names, package names, function names etc.) and if used then compiler will raise an exception.

Kotlin uses fun keyword to define a function, so if we we will try to use it as a variable name then it will be an exception. For example:

fun main() {
   var fun = "Zara Ali"  // Not allowed, throws an exception
   var age = 19          // Valid variable name

   println("Name = $fun")
   println("Age = $age")
}

When you run the above Kotlin program, it will generate the following output:

main.kt:2:7: error: expecting property name or receiver type
   var fun = "Zara Ali"  // Not allowed, throws an exception
      ^
main.kt:2:11: error: expecting ''(''
   var fun = "Zara Ali"  // Not allowed, throws an exception
          ^
main.kt:5:21: error: keyword cannot be used as a reference
   println("Name = $fun")
                    ^

Kotlin keywords have been categorised into three broad categories: (a) Hard Keywords (b) Soft Keywords (c) Modifier Keywords

As a good programming practice, it is highly recommended not to use any of the mentioned keywords to name any identifiers while coding in Kotlin.

(a) Kotlin Hard Keywords

Following is a list of hard keywords and they cannot be used as identifiers:

(b) Kotlin Soft Keywords

Following is the list of keywords (soft) in the context when they are applicable and can be used as identifiers in other contexts:

(c) Kotlin Modifier Keywords

Following is the list of tokens which act as keywords in modifier lists of declarations and can be used as identifiers in other contexts:

   var name = "Zara Ali"
   var age = 19
   var class = "6th"
   var height = 5.3