The "4+1" model is a framework used in software architecture to describe a system's structure. It consists of four main views: the logical view, which focuses on the functionality; the development view, which addresses the software's organization; the process view, which outlines the system's dynamic behavior; and the physical view, which details the hardware and network aspects. The "+1" in the model represents the scenarios view, which illustrates how the system behaves in various situations. This comprehensive approach helps architects and developers understand and communicate the system's design effectively, ensuring all aspects are considered.