Oracle Cloud Infrastructure Compute lets you provision and manage compute hosts, known as instances
. You can launch instances as needed to meet your compute and application requirements. After you launch an instance, you can access it securely from your computer, restart it, attach and detach volumes, and terminate it when you're done with it. Any changes made to the instance's local drives are lost when you terminate it. Any saved changes to volumes attached to the instance are retained.
Oracle Cloud Infrastructure offers both bare metal and virtual machine instances:
1) Bare Metal: A bare metal compute instance gives you dedicated physical server access for highest performance and strong isolation.
2) Virtual Machine: A virtual machine (VM) is an independent computing environment that runs on top of physical bare metal hardware. The virtualization makes it possible to run multiple VMs that are isolated from each other. VMs are ideal for running applications that do not require the performance and resources (CPU, memory, network bandwidth, storage) of an entire physical machine.
An Oracle Cloud Infrastructure VM compute instance runs on the same hardware as a bare metal instance, leveraging the same cloud-optimized hardware, firmware, software stack, and networking infrastructure.

Cloud Horizontal Scaling refers to provisioning additional servers to meet your needs, often splitting workloads between servers to limit the number of requests any individual server is getting. In a cloud-based environment, this would mean adding additional instances instead of moving to a larger instance size.
Cloud Vertical Scaling refers to adding more CPU or memory to an existing server, or replacing one server with a more powerful server.
Reference:
https://cloudcheckr.com/cloud-cost-management/cloud-vs-data-center-what-is-scalability-in-cloud-computing/ Horizontal scaling means that you scale by adding more machines into your pool of resources whereas Vertical scaling means that you scale by adding more power (CPU, RAM) to an existing machine.
An easy way to remember this is to think of a machine on a server rack, we add more machines across the horizontal direction and add more resources to a machine in the vertical direction.

With horizontal-scaling it is often easier to scale dynamically by adding more machines into the existing pool - Vertical-scaling is often limited to the capacity of a single machine, scaling beyond that capacity often involves downtime and comes with an upper limit.

Service Plane is NOT an SLA provided by OCI. See the table below:

https://www.oracle.com/assets/paas-iaas-pub-cld-srvs-pillar-4021422.pdf Enterprises demand more than just availability from their cloud infrastructure. Mission-critical workloads also require consistent performance, and the ability to manage, monitor, and modify resources running in the cloud at any time. Only Oracle offers end-to-end SLAs covering performance, availability, manageability of services.

Changing the Shape of an Instance (Horizontal Scaling)
You can change the shape of a virtual machine (VM) instance without having to rebuild your instances or redeploy your applications. This lets you scale up your Compute resources for increased performance, or scale down to reduce cost.
Autoscaling (vertical scaling)
Autoscaling lets you automatically adjust the number of Compute instances in an instance pool based on performance metrics such as CPU utilization. This helps you provide consistent performance for your end users during periods of high demand, and helps you reduce your costs during periods of low demand.
As load increases, instances are automatically provisioned: the instance pool scales out. As load decreases, instances are automatically removed: the instance pool scales in.

https://docs.cloud.oracle.com/en-us/iaas/Content/Compute/Tasks/resizinginstances.htm