The trendy word is whatever word is currently being overused on the internet this month. It used to be the word “normie”, in 2019 it was “boomer”, and as of 2020, the trendy word is “simp”. If you browse the internet, you will see this word very often.

n. The birth name of somebody who has changed their name. Most commonly attributed to trans people, but can be attributed to any person who has changed their name. (sometimes written as two words: dead name)

v. 1. To call somebody by their deadname.
v. 2. To out somebody's deadname to the public.