League of Legends (LoL) Question: What is sustain?

Sustain is the ability to maintain themselves or allies in lane for longer, in the sense that they don't need to recall to recover health. That can be either through passive regeneration, lifesteal, healing, potions, etc. Some sustain champions are Soraka(healing), Garen and Sett(passive regen), Aatrox (lifesteal).

Sustain, is passive hp restoring, every champ restores some hp passively with no cost, sustain can also be gained throught potions. Laslty champions that have passive sustain, are champions like garen with his passive, sett with his passive, and cho gath with his passive on minion takedown, i cant recall to my mind more.