Veteran is a difficulty level and the hardest in most Call of Duty games, with the exception of Call of Duty: Black Ops III and Call of Duty: Infinite Warfare where the Realistic, Specialist and #YOLO difficulties are introduced, as well as Call of Duty: Modern Warfare, Call of Duty: Black Ops Cold War, and Call of ...
"Recruit" is for Call of Duty beginners or people that just want to enjoy the story. "Regular" is your baseline difficulty setting, not too easy but not too hard. Now, "Hardened" and "Veteran" settings are for more seasoned Call of Duty players who know the ropes and want to have their skills tested.