From Destinypedia, the Destiny wiki
Finishers are a special type of attack added in Shadowkeep. When non-boss enemies are low on health they will start to glow yellow and will have a yellow circle over their heads. If a player gets close to the enemy and presses the button they have binded to finishers, they will go through an animation that will show the player killing the enemy in an interesting way. There are a variety of finishers which can be acquired through the Season of the Undying Season Pass at rank 10 and Eververse Trading Company for silver.
List of Finishers
Note: Exotic Finishers have a † beside them.