**What is the Default and Dedicated Tenancy in AWS?**
1. **Shared (Default) Tenancy**: In this model, multiple customers' instances can run on the same physical hardware. This allows for cost-effectiveness but may lead to resource contention.
2. **Dedicated Tenancy**: With dedicated tenancy, instances run on hardware dedicated exclusively to a single AWS account. This offers greater control over placement and security but comes with higher costs.