Terraform variables are used to define input values for Terraform configurations. They allow users to customize infrastructure deployments by providing different values without modifying the configuration files themselves. Variables help in creating reusable infrastructure code, making it easy to maintain and adjust the infrastructure setup according to different environments or needs.

In OCI DevOps Build Pipeline, the output artifacts generated during the build are temporary and will be discarded unless explicitly stored in a persistent location. By extracting and storing these artifacts in an Artifact Registry (such as OCI Artifact Registry or OCI Container Registry), you ensure that they are available for subsequent stages, such as deployment.
Storing artifacts in a registry provides a persistent location where the deployment pipeline can access them, ensuring the artifacts are available for reliable deployment.

Observability refers to the ability to understand a system's internal state by observing its outputs. It involves metrics, logs, and tracing to provide insights into the system's behavior, which helps in monitoring and identifying issues.