Reference: https://www.oracle.com/a/ocom/docs/cloud/security-overview-100.pdf

Explanation
Horizontal scalingmeans 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.

Reference: https://ocistatus.oraclecloud.com/

Correct. Vertical scaling refers to adding more or faster CPUs, memory, or I/O resources to an existing server, or replacing one server with a more powerful server.