Perl has a number of predefined variables. Most are scalar and start with the "scalar-designation character" $, and are followed by a non-alpha character, which helps to set them apart from user-defined variables.
@_ is a predefined variable you are required to use if you write subroutines that take parameters. Due to this required usage it is the most important predefined variable and the one most commonly used. The @_ array will contain the parameters passed to the subroutine.
