Thank you for your clarification, now I see.
The code responsible for the default text is currently hard-coded in file: /classes/XLite/View/Header.php
protected function getDefaultMetaDescription()
return 'The powerful shopping cart software for web stores and e-commerce '
. 'enabled stores is based on PHP5 with SQL database with highly '
. 'configurable implementation based on templates';
Starting from version 5.2.7 ( coming soon, most likely in October), this value will be editable as a language label. The upgrade of X-Cart v.5 is very simple, so you will be able to get access to this feature easily.
But the default text is inserted, only if you leave blank both brief and detailed description of the product, which does not seem very common for a live online store - text description is good for both your customers and SEO, why would one neglect it?
But right now you need a solution, so you can:
-select "custom" when you're creating the product manually
-use export/import of products to update the products in bulk: the field metaDesc in the CSV file is responsible for it.