I read a comment on an article explaining Web 1.0, 2.0, and 3.0 that I found really summarizes the whole thing:
Web 1: static [Read]
web 2: dynamic [Read/Write]
web 3: programmable[Read/Write/Execute]
I believe this is a great simplified way of expressing what each one is. It reminds me of UNIX-style permission bits for rwx.
In the beginning, there was read-only webpages. These static HTML files sat on webservers and were hyperlinked together.
Then, the read/write era came about. Now pages had Edit buttons; it became as easy to edit a page as it was to read it.
Now, the read/write/execute era is about to begin. Here, the Execute button is going to become as easy as the Edit button. The ability to tap into the CPU cycles of the internet is about to be unfolded.