via a client's request, i'm adding a 'features list' to the products table.

right now i just have question about the Query found in 'main_template_vars.php'

the query is this:
select count(*) as total from zen_products p, zen_products_description pd .....etc.

what does the 'p' and the 'pd' mean following the table names??, unfamiliar w/ such a syntax.

thanks!