What is Trending?

I have to admit that I am not very computer or internet oriented, though I am learning. I was wondering if you can explain to me what it means when something is trending? Also, I am confused about the point of twitter. I appreciate your help and thanks in advance.

Actually, trending is related to twitter. When a tweet is sent it is accompanied by a hashtag. A hashtag lets the reader know something about the tweet. For example, if a boy gives his girlfriend flowers she might tweet about the flowers and use the hashtag #cheezyromantic or #trulove. Tweets associated with those hashtags are grouped and the most popular ones are considered to be trending. Basically, trending is what is hot on twitter and can be driven by demographics or more globally. Popular hashtags that are related to entertainment or businesses translate to advertising dollars and that is why what is trending is often discussed.

Source: K. Depew, News Director