If you can't find it, you can be the first to add a description about it. If a hashtag is about an event you can link to it and add dates so everyone knows what it's about.
On 5-Mar-2019 HTMeaning said A hashtag is a type of metadata tag used on social networks such as Twitter and other microblogging services, allowing users to apply dynamic, user-generated tagging which makes it possible for others to easily find messages with a specific theme or content. Users create and use hashtags by placing the number sign or pound sign or hash symbol (#) front of a word or unspaced phrase in a message. The hashtag may contain letters, digits, and underscores..