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.
Architecture is the “conceptual structure of a system.”
ISO/IEC TR 29108:2013, Information technology — Terminology for intelligent homes
Note: A structure is “the arrangement of and relations between the parts or elements of something complex.” (Google Dictionary)
description of the key elements of a system, their functions, and the interrelationships among the elements.
Road vehicles — Automotive multimedia interface — Part 1: General technical overview
fundamental concepts or properties of a system in its environment embodied in its elements, relationships, and in the principles of its design and evolution.
Systems and software engineering — Architecture description
A highly structured specification of an acceptable approach within a framework for solving a specific problem. An architecture contains descriptions of all the components of a selected, acceptable solution while allowing certain details of specific components to be variable to satisfy related constraints (e.g., costs, local environment, user acceptability). (FISP 201)