This means you can likely trade luxury items (like cider or metal) for other resources (such as food or gold).
In order to find out you can tap your market or mill. Markets require cider to produce extra gold and Mills require metal to produce extra food.
When you mine your gold mines, there's a chance you'll get extra metal units which you can trade in for food.
When you harvest your fruit trees, there's a chance you'll get extra cider units which you can trade in for gold.
When you've got enough of a special resource type (such as cider) a little message will pop up telling you that you can trade (trade available) this at the appropriate building for the appropriate resource.
The research available message means that you can complete a research item and move on to the next item.