Retention Rate: the percentage of members retained over a given period of time.

Lapse Rate (Churn): the percentage of members that discontinue their membership over a given period of time. 

Renewal Rate: the percentage of members that renew their membership over a given time period.

Average Membership Tenure (AMT): the average length of time a member stays with the organization.

Member Lifetime Value (MLV): the measure of the monetary value of members based on the projected length of membership.

Member Acquisition Cost (MAC): the total monetary cost associated with recruiting a new member.

Member Lifetime Value (MLV) to Member Acquisition Cost (MAC) Ratio: the measurement of the relationship between the lifetime value of a member and the cost of acquiring that member.