A cycle is the period in which an individual mentor will meet all their assigned mentees, and in which an individual mentee will meet all their assigned mentors.
For example, assume you have a program where all mentees are assigned 2 mentors, all mentors have 3 mentees, and mentees meet a mentor once per month. In this example, the cycle is the 2 month period it takes for a mentee to meet both of their mentors (2 mentors X 1 mentor per month).
It is called a cycle because this is the amount of time between mentors and mentees repeating sessions with the same individuals.