whats this means in perl?

 
%BDayHeadRow = ( 'BUSDAT', '1', 'ARRDAT', '1', 'SHAWBUSDAT', '2', );
%BDaySize = ( 'BUSDAT', '8', 'ARRDAT', '8', 'SHAWBUSDAT', '6', );
%BDayStartPos = ( 'BUSDAT', '25', 'ARRDAT', '34', 'SHAWBUSDAT', '8', );
%BDayTrail =
  ( 'BUSDAT', 'IMATRL', 'ARRDAT', 'IMATRL', 'SHAWBUSDAT', 'END OF TRS', );

% is an identifier for a hash variable (perl-ish name for associative arrays).
The data is stored as key-value pairs.
Another form of defining a hash that is pleasing to the eye is:

%BDayHeadRow = ( 'BUSDAT'     => '1',
                 'ARRDAT'     => '1',
                 'SHAWBUSDAT' => '2' );

These are called hashes..

Refer here