Deep linking in affiliate marketing programs is the practice by which an affiliate builts directly a link to a specific product page on the merchant website.
Deep affiliate links result in higher conversion rates as the contextual targeting can be more precise and focused on a single product and because the user is led directly to the product he is interested in.
Some merchants favor the practice and make deep linking more easy for affiliate by offering deep linking tools. This kind of tools enables affiliates to obtain their deep affiliate link by entering the product in a search box.
Below, an example of deep linking tool: