[qualiteam]

You can change the text in the Translations section of your site back end - search for "default-meta-description" label.

However, this will change the text for all site pages except product/category/brand pages. If you want to change this text on the cart page only, you are to create a custom module that adds getMetaDescription() method to \XLite\Controller\Customer\Cart class and makes it return the text that you need. You can do it via CustomSkin module too (i.e. without creating a new custom module).