Common jargon used by players of Training Camp Level 20 (research). Not only do you have to get the building level up to level 20, you also have to get the research (Legendary Training) Researched. What comes is the epitome of what can be achieved for hero acquisition by C2P and F2P right from the comfort of their own base. In this training, for each 2-day session of 297K Food, 100 Recruits, and I think a very common Ascension Material (Leather Armor or Rugged Cloth, can’t remember) and you have a chance to acquire 3*-5* heroes (obviously the chance for 3* being the highest, followed by 4*, then 5* being lowest).
It is what I also refer to as homegrown heroes (e.g. not acquired by gem summons, token summons).
For a list of other commonly used jargons, I invite you to check out the below thread compiled by @JonahTheBard.