DATABASE: products
-- TABLE: cats
-- -- COLUMN: id
-- -- COLUMN: cat
-- TABLE: products
-- -- COLUMN: id
-- -- COLUMN: name
-- -- COLUMN: cat
You select the row id from the cats table where cat = (what the user inputting?). You then select all from products where cat = (cat id).
That way you can add and remove categories, and you call pull them all out and put them into a select menu in HTML or something.
With regards to meta tags and such:
Code:
<meta name="description" content="High quality <?php echo $category; ?> products at low prices!" />
(obviously that's just the general drift lol).