The term deep linking was first used in the context of search engine optimization (SEO) to describe the practice of linking to a website's internal pages rather than to its homepage. As an SEO strategy, deep linking allows site users to more easily find the specific content they're looking for while simultaneously improving a website's relevancy in search engine results by connecting keyword-rich hyperlinks on one interior site page to keyword-rich content on another internal page [source: Patel].
In the world of mobile apps and app development, deep links are essentially URLs for the inside of an app [sources: Deeplink, MobileDeepLinking]. Just as deep links on a website help bring users directly to the content they are looking for, deep linking between apps connects a unique URL to a specific action, connecting users to the content they're seeking [source: MobileDeepLinking]. For example, if a user with a travel app installed on his or her phone does a Google search for "hotel deals," clicking on a link in the search results could open the travel app instead of a web page [source: Hsiao].
To put it another way, deep linking understands which types of links are utilized by which apps [source: Lardinois]. Today, if you have a banking app installed on your phone, and you receive an email notifying you that your online statement is available, clicking on the "View your statement" link in the email will take you to your bank's website, where you need to go through the standard login process and navigate to the statement online. With deep linking, clicking on the same link in an email on your phone would instead launch your banking app, taking you directly to the information you're looking for.