bus factor

The bus factor is the minimum number of team members that have to suddenly disappear from a project before the project stalls due to lack of knowledgeable or competent personnel. It measures how fragile a system is. If the answer is one, you don’t have a team - you have a single point of failure. In software and product development, this concept measures the risk based on how knowledge and responsibility are distributed. The higher the number, the safer the system.