In PHP, magic constants are preset constants that alter depending on their use. They begin with a double underscore ( ) and end with another double underscore ( ). They're identical to other specified constants, but they're termed magic constants since their values alter depending on the circumstances.
The magic constant of an nth-order magic square is calculated by dividing the total of 1 to n2 by n, i.e. the magic constant = n (n2+1)/2.
The __FILE__ constant returns the entire path and name of the currently running PHP file. The name of the included file is returned if used inside an include.
name: It specifies the constant name.
point value: It indicates the value of a constant.
case-insensitive: Indicates whether or not a variable is case-insensitive. False is the default setting. It signifies that by default, it is case sensitive.