Damage cycle is the term usually used to refer to an instance of health damage incurred by a character or creature. Usually, it is only used in reference to spells that inflict multiple instances of damage, and rarely in reference to a isolated instance of health damage. Some spells that exhibit this trait of multiple damage cycles are Bone Shatter (1106), Spike Thorn (616), and Disintegrate (705).
An example would be the following with the use of the Bone Shatter spell.
CS: +XXX - TD: +XXX + CvA: XXX + d100: +87 == +164 Warding failed! The half-elven robber shudders with sporadic convulsions as pearlescent ripples envelop his body. The half-elven robber is crushed for 62 points of damage! ... 50 points of damage! <-Damage cycle Massive blow to back separates vertebrae! It is knocked to the ground! The half-elven robber is stunned! ... 25 points of damage! <-Damage cycle Strong blow to abdomen!