Instagram's Threads app, inspired by Twitter, is testing the use of tags to categorize posts by interest or theme, although the tags will not display the "#" symbol. The tag feature will initially be tested in Australia, with more countries to follow soon, while users can create tags by tapping the # button or typing the symbol followed by text. Unlike Twitter, Threads will only allow one tag per post, which aims to reduce spam and attention-seeking behavior but may limit users in certain scenarios.