Differentiate between variables and constants in PHP

A few differences between variables and constants in PHP are given below:

Constants Variables
There is no need to write a dollar ($) sign before a constant A variable must be written with the dollar ($) sign
Constants can only be defined using the define() function Variables can be defined by simple assignment
Constants may be defined and accessed anywhere without regard to variable scoping rules. In PHP, functions by default can only create and access variables within their own scope.
Constants cannot be redefined or undefined. Variables can be redefined for each path individually.