PHP has a set of keywords that are reserved words which cannot be used as function names, class names or method names.

These words have special meaning in PHP. Some of them represent things which look like functions, some look like constants, and so on - but they're not, really: they are language constructs.

keywords are allowed as property, constant, and method names of classes, interfaces and traits, except that class may not be used as constant name.

Keywords

abstract	Declare a class as abstract
and	A logical operator
as	Used in the foreach loop
break	Break out of loops and switch statements
callable	A data type which can be executed as a function
case	Used in the switch conditional
catch	Used in the try..catch statement
class	Declare a class
clone	Create a copy of an object
const	Define a class constant
continue	Jump to the next iteration of a loop
declare	Set directives for a block of code
default	Used in the switch statement
do	Create a do...while loop
echo	Output text
else	Used in conditional statements
elseif	Used in conditional statements
empty	Check if an expression is empty
enddeclare	End a declare block
endfor	End a for block
endforeach	End a foreach block
endif	End an if or elseif block
endswitch	End a switch block
endwhile	End a while block
extends	Extends a class or interface
final	Declare a class, property or method as final
finally	Used in the try...catch statement
fn	Declare an arrow function
for	Create a for loop
foreach	Create a foreach loop
function	Create a function
global	Import variables from the global scope
goto	Jump to a line of code
if	Implement an interface
implements	Implement an interface
include	Embed code from another file
include_once	Embed code from another file