# Definitions
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 The AWS Well-Architected Framework is based on six pillars: operational excellence, security, reliability, performance efficiency, cost optimization, and sustainability. SaaS adds a new dimension of considerations to each of these pillars. The multi-tenant nature of SaaS applications, requires architects to reconsider how they address security, operational efficiency, stability, and agility of their SaaS environments. In this section, we will present an overview of the SaaS concepts that will be used throughout this document. There are 10 areas you should consider when building a SaaS architecture. 

**Topics**
+ [Tenant](tenant.md)
+ [Silo, Pool, and Bridge Models](silo-pool-and-bridge-models.md)
+ [SaaS Identity](saas-identity.md)
+ [Tenant Isolation](tenant-isolation.md)
+ [Data Partitioning](data-partitioning.md)
+ [Noisy Neighbor](noisy-neighbor.md)
+ [Tenant Onboarding](tenant-onboarding.md)
+ [Tenant Tiers](tenant-tiers.md)
+ [Tenant Activity and Consumption](tenant-activity-and-consumption.md)
+ [Tenant-Aware Operations](tenant-aware-operations.md)