The phrase describes a resource, typically a comprehensive and reliable publication, that serves as an indispensable support or guide for a particular activity or subject. For example, a detailed technical manual could be considered such a resource for engineers, providing essential information and procedures when needed.
Its value lies in its ability to provide readily accessible expertise and assistance. Historically, reference books, handbooks, and comprehensive guides have played this role, offering crucial information and best practices that enable individuals and organizations to accomplish tasks efficiently and effectively, reducing errors and improving overall outcomes. The availability of such a resource can significantly enhance productivity and knowledge retention.