Hi Pete,
You might want to read:
http://www.oreillynet.com/pub/a/orei...is-web-20.html
Yes web 2.0 is a term coined to describe an idea. It was coined by Tim O Reilly - the publisher of all those web programming books.
This snapshot pretty much gives you the difference between web and web 2.0:
Web 1.0 --> Web 2.0
DoubleClick --> Google AdSense
Ofoto --> Flickr
Akamai --> BitTorrent
mp3.com --> Napster
Britannica Online --> Wikipedia
personal websites --> blogging
evite --> upcoming.org and EVDB
domain name speculation --> search engine optimization
page views --> cost per click
screen scraping --> web services
publishing --> participation*
content management systems --> wikis
directories (taxonomy) --> tagging ("folksonomy")
stickiness --> syndication
* List taken from the above linked article. Bold is my emphasis.