VirtualBox: A virtual machine created with VirtualBox contains simulated hardware, an installed OS, and installed applications. If you want multiple VMs, you need to simulate all of that for each.

Docker containers virtualize the application, but use their host's hardware and kernel without simulating it. This makes containers smaller and lighter.

VMs are good if you care about the hardware and the OS, for example to create different testing environments. Containers are good if you want to run many in parallel, for example to provide services on a server. Because they are lightweight, it's also easy to share containers. You can choose from a wide range of preconfigured containers, and directly use them or customize them to your liking.