Explanation/Reference:
Large-Building LANs
Large-building LANs are segmented by floors or departments. The building-access component serves one or more departments or floors. The building-distribution component serves one or more building- access components. Campus and building backbone devices connect the data center, building-distribution components, and the enterprise edge-distribution component. The access layer typically uses Layer 2 switches to contain costs, with more expensive Layer 3 switches in the distribution layer to provide policy enforcement. Current best practice is to also deploy multilayer switches in the campus and building backbone.
Cisco Enterprise Architecture Model
Core
Distribution
Access
Cisco Press CCDA 640-864 Official Certification Guide Fourth Edition, Chapter 3