Trends are determined by an algorithm and, by default, are tailored for you based on who you follow, your interests, and your location. This algorithm identifies topics that are popular now, rather than topics that have been popular for a while or on a daily basis, to help you discover the hottest emerging topics of discussion on Twitter.
You can choose to see Trends that are not tailored for you by selecting a specific Trends location on twitter.com, iOS, or Android (instructions below). Location Trends identify popular topics among people in a specific geographic location.
You may notice that some trends have # sign before the word or phrase. This is called a hashtag and is included specifically in Tweets to mark them as relating to a topic, so that people can follow the conversation in search.
Yes, when signed into your account on the twitter.com, iOS, or Android, Trends will be tailored for you based on your location and who you follow. There will be many world and local news events and conversations that will appear in your trends regardless of your personalization.