Discontinued products are products that the suppliers are no longer supplying. Such products will show an Orange "Discontinued" label next to them.
In the quote, when you want to search and add products, discontinued products will show up in the search.
If you want to clean up the catalog by removing the discontinued products, do the following:
Go to Catalog > My Products in the left navigation menu.
Apply the Discontinued filter to the products. Now, you will see only discontinued products.
Select all or required products and click "Remove from my products" under the Action on selected button on the top-right.

