In perl, a hash is differentiated from other data types with the '%'-sign. A hash is essentially an array whose elements are named. This makes it easy to access any specific element given that name. In common perl parlance, the element's name is called the "key" and the element is called the "value".
As mshumphr demonstrates above, a hash element is accessed with the '$'. There are two basic forms to dereference the data:
$value = $hash{key}
$value = $hash->{key}
In older per documentation, Hashes used to be called "associative arrays".
For more information, see the perldata manpage.