A "trending hashtag" refers to a popular topic or keyword that is widely used on social media platforms at a particular time. It often represents a discussion or trend that many people are talking about or interested in. Full definition
Nothing looks more cheesy and self - serving than brands trying to take every single trending hashtag and relate back to themselves. (inc.com)
That was one of the top trending hashtags on Twitter yesterday, after more than $ 1 trillion was wiped from Asian markets, sending the Dow plunging again (it closed for the day down 588 points). (inc.com)
The Facebook Live Giphy feature puts you in a virtual newsroom with trending hashtags for GIFs that you can tap and «report on.» (engadget.com)