In programmer-speak, literals are values that are entered in the source code explicitly.
For example, in the expression $x = 5 the number 5 is a literal.
There are two types of literals to consider:

1. Perl Numeric Literals
   
2. Perl String Literals

Numeric literals are frequently used and represent a number that your program will need to work with.
Most of the time you will use numbers in ten-base expression.
Perl will also let you use base 8 (octal) or base 16 (hexadecimal).

1. In octal notation or base eight, when you see the value 15 it signifies (1 * 8) + 5 or 1310.
2. In hexadecimal notation when you see the value 15 it signifies (1 * 16) + 5 or 2110.
   Base 16 needs an additional 6 characters besides the digits 0 to 9 so that each position can have a total of 16 values.
   The letters A-F are used to represent 11-16.

So the value BD16 is equal to (B16 * 16) * D16 or (1110 * 16) + 1310 which is 17610.