Definition of "trending"

trending¹

verb
1. present participle and gerund of trend
adjective
not comparable
1. (Internet, marketing) Popular or becoming more popular.
  Quotations
  […] the only conversation most people can keep track of is what’s trending on social media.
  2015 September 28, Yesha Callahan, “Social Media Is Driving the TV Conversation”, in The New York Times

trending²

noun
plural trendings
1. A trend, or inclination in a particular direction.