Some people have some pretty funny ideas about what the term "web 2.0" means.  Many people are even coining their own definitions for web 2.0, saying that it refers to a "semantic web" or a "machine learning web", etc.  This all stems from the fact that many people hear the term, but don't know what it means.  The term actually originated from a progamming method called AJAX (asynchronous javascript and XML) that was the first widely-adopted way of programmatically getting around the limitation of waiting on page reloads to and from the server as you navigated around a website and performed searches, form submissions, and other operations.

Simply put, Web 2.0 is a term used to refer to applications that uses AJAX or a similar methodology to communicate with the server in the background, without requiring page reloads.

In other words, the old way of doing things was to have the user fill in a form, click submit, the page reloads and the server does something with it (like register an account, perform a search, etc).

The new way is to have user input that is submitted communicated to the server in the background, so you get a little icon that signifies your data is being submitted, but the page does NOT reload. When the response is received back from the server, the page that is ALREADY loaded in your browser knows how to handle the response and update the interface on your end. The result: You only have to load a web page once, and from there on it functions like a normal software application in that communication is sent to and from the server transparently, and you don't have to wait on page reloads between each command/operation. That is web 2.0.

If you see someone else referring to Web 2.0 as something different, or even making up their own definition, please take a moment to correct them.  The truth is, we are all still developing web 2.0 because there are a vast number of web applications out there that STILL use the old methodology of submitting the form, waiting on the page to reload from the server, then showing the next form to the user, submitting, waiting...  We've got a long way to go before web 2.0 is fully implemented in the majority of websites out there, and already I see people not only incorrectly using the term Web 2.0 (which takes focus away from the goal of getting rid of page reloads on the web), but in fact even trying to coin their own definitions for Web 3.0, 4.0 and up...  which don't even exist!