What are products in Shopify classified as 'Not available on the online store'?

Once a product is active or published in Shopify, its visibility can be limited across various channels including your online store.

For products to be visible in collections, for your online visitors, the 'Online Store' sales channel should be enabled & its status should be 'Active'. 

If this is not yet enabled, they can still be pre-merchandised by enabling 'Include products unavailable on online store', within the Tagalys dashboard.