Deep link
A link that opens a specific screen inside an app rather than a web page.
A deep link addresses a location inside a native app — a particular product, profile or screen — rather than a website. From a QR code, it is what makes a scan open the app itself instead of a browser page about the app.
Universal and App Links. Modern deep links use ordinary HTTPS URLs that
the operating system recognises as belonging to an installed app (Universal Links on iOS,
App Links on Android). If the app is installed it opens; if not, the same URL loads in the
browser. That graceful fallback is why these are preferred over custom
myapp:// schemes, which simply fail when the app is absent.
The QR pattern. A dynamic code can detect the scanning device and route accordingly: iOS to the App Store, Android to Google Play, anything else to a web page. Doing this with a static code is impossible, because a static code encodes exactly one destination.
In practice
A cinema puts a code on its poster. An iPhone with the app installed opens straight to that film's showtimes. An iPhone without it goes to the App Store listing. An Android phone goes to Google Play. A laptop camera gets the website.
Four outcomes, one printed code — only possible because the code is dynamic and the routing happens server-side at scan time. A static code would have to pick one of those four and fail the other three.
Questions
Why not use a myapp:// scheme directly?
Because it fails with an error page when the app is not installed, which is most people. Universal Links and App Links use ordinary HTTPS URLs that fall back gracefully to the web.
Can I tell how many people had the app installed?
Partially. The platform records the device type it routed; combined with app-side attribution you can usually reconstruct install-versus-store splits.