However, it is recommended to name the constants in all uppercase letters. Class constants are case-sensitive.

A class constant is declared inside a class with the const keyword. Class constants can be useful if you need to define some constant data within a class. In PHP, static and const are two different things. Their syntax: class Test { const INT = "/^\d+$/"; } Because they're constant, they're immutable. const denotes a class constant.

PHP - Class Constants. Constants cannot be changed once it is declared. They're different than normal variables as they don't have the '$' in front of them, and can't have any visibility modifiers (public, protected, private) before them.