Generally refers to "how many people can continue to develop/support this software if original maintainer (and close co-developers) get hit by a bus."
The number of developers that can be suddenly and totally lost from a project (e.g., by being hit by a bus) without the project itself becoming unable to proceed effectively.
Generally refers to "how many people can continue to develop/support this software if original maintainer (and close co-developers) get hit by a bus."