The article explores different ways to summarize popular topics on Twitter, like why "SXSW" is trending. By looking at tweets, normalized tweets, and web content linked from tweets, the researchers found that using a mix of sources can help create clearer summaries. They used a concept-based optimization framework to evaluate the quality of the summaries and found that different sources and types of topics can affect performance. The study also identified challenges in summarizing topics from user-contributed content on the internet.