What are some good topics for a process speech?

Which words/phrases aren't tracked in Twitter Trending Topics?

• I imagine that the many commonly used words used in speech (I, you, the, social, coffee, etc.) aren't tracked and I know that Trending Topics never include usernames (so TT don't include RT'd usernames like Mashable). But there was a time when Follow Friday was on a blacklist of sorts and not included in TT before it reappeared despite it's continued high usage. Are there certain names, words or phrases that are deliberately kept off of the TT list because of their frequency or the nature of their content? I'm not asking to criticize the selection process, just to understand why some odd topics make the Top 10 while others that seem to have quite a buzz don't.

• Answer:

  Trending does not mean that the topic has the highest volume of tweets but that it temporarily has a higher frequency among other not common topics, so I guess Twitter uses something like https://en.wikipedia.org/wiki/Tf%E2%80%93idf I think people outside Twitter's engineering core cannot accurately reply the question, so this was my guess.