Hashtag hijacking refers to the act of taking over a popular or trending hashtag on social media and using it for a different purpose than its original intent. This can be done by individuals, groups, or companies in order to gain attention, promote their own agenda, or disrupt the conversation. It often involves using the hashtag in a sarcastic or ironic manner, causing confusion or controversy among users. Hashtag hijacking can be a strategic marketing tactic, but it can also be seen as a form of online vandalism.