• (named) function something of the form Name(Args) usable as EXPR, that means returning a value at runtime. Parens can be omitted if precedence is clear. Arguments - if any - must follow to the right, either as one UNARY value or as comma separated LIST.
• builtin : a named function in the language core. The name is a reserved keyword. Some may have special parsing rules for arguments and special context, such that they can't be replicated with sub (PROTOTYPE) { BLOCK }
• operator symbols acting like functions by returning values but with "surrounding" (not necessarily following) arguments, special parsing and precedence like 2 * 3 . See perlop and overload
• named operators like xor have an alphanumeric IDENTIFIER as "symbol". NB: some builtin functions are sometimes documented as "operators" (it's just a huge subgroup with a more standard syntax)
• statement keywords anything requiring void context. I.e. can't be used in an expression (without do ). It usually follows a semicolon and is used for side-effects . Most at compile time like like use
• Some of them are documented as "function-like keywords" because they parse like functions like my but are primarily used for declaration (a compile time side effect)

Please expand/correct me. ..

EDIT

N.B. some keywords fall into multiple categories, depending on usage.

sub name { Block } is a statement declaring a subroutine at compile time.

$code = sub { Block }; is a builtin function returning a coderef at runtime.