I think this terminology is left-over from Sun's
Suntone architecture. In this concept, Sun organized a design on three dimensions: Layers, Tiers, and Systemic Qualities.
Systemic qualities are the non-functional requirements, such as the big seven topics tested on the SCEA exam: scalability, maintainability, reliability, availability, extensibility, performance, manageability, and security.
Tiers are major logical and physical components through which processing passes, such as client, web server, app server, database, etc.
Layers are design components grouped by level of abstraction. The bottom layer might be hardware. The operating system might be a layer on hardware. Sharable libraries might be a layer on that, then the app server on that, then EJBs on top.