Explanation
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