Constants are similar to variables in that they can be assigned a value,
but unlike variables, they cannot be changed once assigned. Also unlike
variables, they do not use dollar signs and the values are assigned with the
define() function rather than the equal sign.
In the below example, the FAV_MUSIC constant is set to metal because my favorite
music is metal. Someone came along and tried to change it to country, but like
Tenacious D said, you can't kill the metal.
The Metal
My favorite music is metal.
Someone tried to change my favorite music to country,
but it's still metal