Constants in PHP are named values that cannot change during the execution of a script. They are case sensitive like variables but are defined separately.
You can use the
const keyword to define a constant.
const NAME = 'Ryan';
The convention in PHP is to use an uppercase name for all constants. You're also allowed to use underscores and numbers.
Another method for defining constants is the
define() function. This function accepts the name of the constant and it's value.
It's highly likely you'll see this in PHP code, however the more modern approach is using the
const keyword from above.