A layer is “a collection of objects of the same hierarchical rank.” (ISO/IEC 16500-4:1999, Information technology — Generic digital audio-visual systems — Part 4: Lower-layer protocols and physical interfaces)
A layer is a conceptual or logical division of a system, which is composed of elements. If a system comprises multiple layers, they are typically organized in a hierarchical structure where elements in a layer (N) interact directly only with elements in the adjacent higher layer (N+1) or the adjacent lower layer (N-1) of a system through services provided by each layer.
description of the key elements of a system, their functions, and the interrelationships among the elements. ISO 22902-1:2006, Road vehicles — Automotive multimedia interface — Part 1: General technical overview
conceptual structure of systems that are to communicate with each other. ISO/IEC TR 15044:2000, Information technology — Terminology for the Home Electronic System (HES)
Single Sign-On (SSO)
access control mechanism where a user logs on once and gains access to a number of applications and services without being prompted to log in again at each of them. ISO/IEC TR 26927:2011, Information technology — Telecommunications and information exchange between systems — Corporate telecommunication networks — Mobility for enterprise communications
function enabling a user to access a number of websites or applications with a single User ID and password. ISO 20488:2018, Online consumer reviews — Principles and requirements for their collection, moderation and publication