Health or Mental Integrity is the overall physical and psychological wellbeing. In the context of the Telepath games, health is equal to the amount of damage a unit can take before dying or otherwise be defeated. Health is increased by increments of two when Psy Defense is upgraded.
Health is able to be replenished through the use of psychokinetic shields, such as Mind Shield. A few Psy Healers can even learn how to increase the maximum health of with a unit with a Static Shield.