A fault domain is a grouping of hardware and infrastructure within an availability domain. Each availability domain contains three fault domains. Fault domains provide anti-affinity: they let you distribute your instances so that the instances are not on the same physical hardware within a single availability domain. A hardware failure or Compute hardware maintenance event that affects one fault domain does not affect instances in other fault domains. In addition, the physical hardware in a fault domain has independent and redundant power supplies, which prevents a failure in the power supply hardware within one fault domain from affecting other fault domains.
To control the placement of your compute instances, bare metal DB system instances, or virtual machine DB system instances, you can optionally specify the fault domain for a new instance or instance pool at launch time. If you don't specify the fault domain, the system selects one for you. Oracle Cloud Infrastructure makes a best-effort anti-affinity placement across different fault domains, while optimizing for available capacity in the availability domain. To change the fault domain for an instance, terminate it and launch a new instance in the preferred fault domain.
Use fault domains to do the following things:
Protect against unexpected hardware failures or power supply failures.
Protect against planned outages because of Compute hardware maintenance.
Reference:
https://blogs.oracle.com/cloud-infrastructure/using-availibility-domains-and-fault-domains-to-improve-application-resiliency

Oracle offers several different service level agreements as defined in this section (Service Level Agreements).Service level agreements range from least restrictive (data plane) to more restrictive (control plane) to most restrictive (performance).
Reference:
https://www.oracle.com/assets/paas-iaas-pub-cld-srvs-pillar-4021422.pdf

Oracle's mission is to build cloud infrastructure and platform services for your business to have effective and manageable security to run your mission-critical workloads and store your data with confidence.
Oracle Cloud Infrastructure offers best-in-class security technology and operational processes to secure its enterprise cloud services. However, for you to securely run your workloads in Oracle Cloud Infrastructure, you must be aware of your security and compliance responsibilities. By design, Oracle provides security of cloud infrastructure and operations (cloud operator access controls, infrastructure security patching, and so on), and you are responsible for securely configuring your cloud resources. Security in the cloud is a shared responsibility between you and Oracle.
In a shared, multi-tenant compute environment, Oracle is responsible for the security of the underlying cloud infrastructure (such as data-center facilities, and hardware and software systems) and you are responsible for securing your workloads and configuring your services (such as compute, network, storage, and database) securely.
In a fully isolated, single-tenant, bare metal server with no Oracle software on it, your responsibility increases as you bring the entire software stack (operating systems and above) on which you deploy your applications. In this environment, you are responsible for securing your workloads, and configuring your services (compute, network, storage, database) securely, and ensuring that the software components that you run on the bare metal servers are configured, deployed, and managed securely.
More specifically, your and Oracle's responsibilities can be divided into the following areas: