folks' tweets, but instead fleets were generally used by users who already tweeted a lot. The company stated that their spot at the top of the screen would now be occupied by currently active Spaces from the user's feed. Curation Trending topics A word, phrase, or topic that is mentioned at a greater rate than others is said to be a "trending topic". Trending topics become popular either through a concerted effort by users or because of an event that prompts people to talk about a specific topic. These topics help Twitter and their users to understand what is happening in the world and what people's opinions are about it. The Twitter web interface displays a list of trending topics on a sidebar on the home page, along with sponsored content. Trending topics are sometimes the result of concerted efforts and manipulations by fans of certain celebrities or cultural phenomena, particularly musicians like Lady Gaga, Justin Bieber, Rihanna and One Direction, and novel series Twilight and Harry Potter. Twitter has altered the trend algorithm in the past to prevent manipulation of this type with limited success. Twitter also censors trending hashtags that are claimed to be abusive or offensive. Twitter censored the #Thatsafrican and #thingsdarkiessay hashtags after users complained that they found the hashtags offensive. Lists In late 2009, the "Twitter Lists" feature was added, making it possible for users to follow ad hoc lists of users instead of individual users. Moments In October 2015, Twitter introduced "Moments"—a feature that allows users to curate tweets from other users into a larger collection. Twitter initially intended the feature to be used by its in-house editorial team and other partners; they populated a dedicated tab in Twitter's apps, chronicling news headlines, sporting events, and other content. In September 2016, creation of moments became available to all Twitter users. Algorithm An October 21, 2021, report based on a "long-running, massive-scale randomized experiment" that analyzed "millions of tweets sent between 1 April and 15 August 2020", found that Twitter's machine learning algorithm amplified right-leaning politics on personalized user Home timelines. The report compared seven countries with active Twitter users where data was available—Germany, Canada, the United Kingdom, Japan, France, and Spain—and examined Tweets "from major political groups and politicians". Researchers used the 2019 Chapel Hill Expert Survey (CHESDATA) to position parties on political ideology within each country. The "machine learning algorithms"—introduced by Twitter in