When you use Terraform, you are going to want to know the name of the region to use. I’ll show you in a easy-to-see way.
oci iam region list \
--query "data[*]".{'key:key,name:name'} --output table
The command above shows the following output.
+-----+----------------+
| key | name |
+-----+----------------+
| AMS | eu-amsterdam-1 |
| BOM | ap-mumbai-1 |
| DXB | me-dubai-1 |
| FRA | eu-frankfurt-1 |
| GRU | sa-saopaulo-1 |
| HYD | ap-hyderabad-1 |
| IAD | us-ashburn-1 |
| ICN | ap-seoul-1 |
| JED | me-jeddah-1 |
| KIX | ap-osaka-1 |
| LHR | uk-london-1 |
| MEL | ap-melbourne-1 |
| NRT | ap-tokyo-1 |
| PHX | us-phoenix-1 |
| SJC | us-sanjose-1 |
| SYD | ap-sydney-1 |
| YNY | ap-chuncheon-1 |
| YUL | ca-montreal-1 |
| YYZ | ca-toronto-1 |
| ZRH | eu-zurich-1 |
+-----+----------------+
It is possible to view available regions from the web console though it’s paged. Click the region -> Manage Regions to view.

It is wise to subscribe to only the regions you are going to use. Subscribing to regions do not cost at all, however.