Reference: https://medium.com/oracledevs/scaling-your-oci-web-server-203895180102

Explanation
For more information on Oracle Cloud Infrastructure Free Tier refer below official documentation
https://docs.cloud.oracle.com/en-us/iaas/Content/FreeTier/freetier.htm?Highlight=Free%20Tier Exadata DB Systems aren't a part of the free tier:

Remote VCN Peering is the process of connecting two VCNs in different regions so that their resources can communicate using private IP addresses.

Explanation
A fault domain is a grouping of hardware and infrastructure within an availability domain. Each availability domain contains three faultdomains. 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 onefault 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.
Usually fault domains to do the following things:
1) Protect against unexpected hardware failures or power supply failures.
2) Protect against planned outages because of Compute hardware maintenance.

Reference:
https://www.youtube.com/watch?v=XXqTGF8G0dk&list=PLKCk3OyNwIzuHYigVbdtDOZOfChcotfj2&inde x=6