Health is used to denote the life force for all champions. When an opponent hits you with an ability that does damage, your health bar drops for that amount of damage. When your health bar depletes completely, your character dies and remains unplayable until the next round. The maximum health for any given champion is unique, but generally the beefier champions will have more health and the more fragile champions will have less (see their specific page for values). That being said, the topic gets a little more complex, as there are some limitations on how much you can heal. The two types of health are recovery health and real health.
A unique aspect of Battlerite is that when your health dips below a certain threshold (buffer of 40 hp is maintained between real and recovery health), you become unable to be healed past that threshold. Your new maximum health at this point is called your recovery health. For example, if you have 250hp max hp and droped to 200hp, then you end up with 240 recovery hp, meaning you are only able to be healed up to 240hp. The only exception to this is called true healing, which is currently only available by picking up health orbs(+6 real health) or destroying the Energy Rune(+10 real health).
There are many ways to recover health. Here is a generic list: