You're thinking of the Guest Additions which is part of the base Virtualbox package and free for commercial use.
The (commercially licensed) Extensions pack provide "Support for USB 2.0 and USB 3.0 devices, VirtualBox RDP, disk encryption, NVMe and PXE boot for Intel cards"[1] and some other functionality e.g. webcam passthrough [2]. There may be additional functionality enabled by the Extension pack I cannot find at a glance, but those are the main things.
A tad offtopic, but on my 2017 Macbook Pro the "pack" was called VMWare Fusion.
With my MBP as host and Ubuntu as guest, I found that VirtualBox (with and without guest extensions installed) had a lot of graphical performance issues that Fusion did not.
You're thinking of the Guest Additions which is part of the base Virtualbox package and free for commercial use.
The (commercially licensed) Extensions pack provide "Support for USB 2.0 and USB 3.0 devices, VirtualBox RDP, disk encryption, NVMe and PXE boot for Intel cards"[1] and some other functionality e.g. webcam passthrough [2]. There may be additional functionality enabled by the Extension pack I cannot find at a glance, but those are the main things.
[1] https://www.virtualbox.org/wiki/Downloads [2] https://www.virtualbox.org/manual/ch01.html#intro-installing
A tad offtopic, but on my 2017 Macbook Pro the "pack" was called VMWare Fusion.
With my MBP as host and Ubuntu as guest, I found that VirtualBox (with and without guest extensions installed) had a lot of graphical performance issues that Fusion did not.