Constants

Explaination:

Constants in PHP are identifiers for simple values that cannot be changed during the execution of a script. Unlike variables, constants are globally scoped and do not use the $ prefix. They are typically defined using the define() function or the const keyword.

The key differences between constants and variables:

• Constants cannot be changed once they are defined
• Constants are automatically global across the entire script
• Constants are typically written in all uppercase letters
• Constants can only store scalar data (boolean, integer, float, and string)