As friends said above, its otherwise called as associative
array. It has lot of advantages over perl.

Here we can keep the values in a structured way, that
structured way comes from key-value pairs.

Eg: (The syntax given above are also correct, but the below
representation is much better in look and feel)

my %hash_example = ( a => 10,
                     b => 20,
                     c => 30 );  
keys   : a,b,c
values : 10,20,30

Features of Hash :
##################
1) Keys should always be unique where as values may not be
unique

(Right)
my %hash_example = ( a => 10,
                     b => 10,
                     c => 10 );

(wrong)
my %hash_example = ( a => 10,
                     a => 20,
                     a => 30 );

2) keys (%hash_example) will return an array containing only
keys

my @keys = keys(%hash);

3) similary for values
my @values = keys(%values);