Trending topics are a series of keywords that are most mentioned on Twitter at that time. Trending topics are a way to see where a lot is talked about on Twitter, and each country also has its own trending topics. Nowadays, there is a lot of talk about trending topics outside of Twitter, but the idea remains the same: these are subjects that are often talked about in any way whatsoever. On Twimmer is a nice overview to see what the trending topics are.
A hashtag is a way to catagoriseren messages on Twitter. Much is used at events/conferences to make all messages about an event easy to find. This is also frequently used in news items (#schipholcrash). A hashtag is a hash (#) with the tag behind it. It descends from IRC where you can access a certain channel with a #. The hashtag is already very well established in everyday life and is used everywhere. Read More
Twitter is a service/website that works a bit like MSN Messenger and SMS. You can say in 140 characters what you are doing at the moment, are reading, or are planning to go. So far it looks like SMS. All the people who follow you (in your friends list) see that message, and Kunen may respond to it (this is the comparison with MSN Messenger). You can enter these messages on the website, but there are also a lot of other tools that you can use to customize your status (Windows/Linux/Mac/Mobile/etc.). Read More