There have been numerous ways for users to interact with web pages on mobile phones. Historically, users navigated the mobile web by pressing physical buttons (arrow keys, soft keys, etc.), while some devices required a stylus.
In the last several years, devices with touch-enabled screens have been adopted at such a rapid rate that touch interaction has become ubiquitous. Now we have tablets that take input not only from touch, but from keyboards and mousepads using optional peripherals.
So what does it mean to you as a web developer? It means you need to detect the correct user input method, and design the correct user experience into your web apps.