In Shopify, it's possible to add custom tags when editing a product, as shown in the example below:
These tags can be imported as custom product attributes which can then be uploaded into marketplaces, e.g. as eBay Item Specifics. There are limitations to how we can turn tags into properly-formed product attributes however: the tag must be in the form <name> and <value> so in the above example, 'sale' will be ignored whereas the other tag appears to be for a product attribute called 'season' with value 'winter'. Please note that eBay requires these tags to be case specific eg Type:Coffee Table not type:coffee table.
To tell us that you want to import tags, go to Settings > Shopify Feed > Map Product tags and go to "Extract product attributes from tags". Here you need to enter the delimiter character that separates the name and value portions, in the above example it's a colon ':', and then you'll then need to trigger a re-import of your product feed to refresh the data.
Note that if this process imports tags that you DO NOT want to use, you can exclude them by going to Settings > Administration and entering the attribute names in the field "Remove these attributes from products", one per line, and then triggering a re-import of the feed to refresh the data.
eBay Item Specifics - How to map your product attributes to eBay Item Specifics.