This short post answers the question, "What key is the Host key in Oracle's VirtualBox on Windows, Mac, and Linux?"
What Key is the Host Key in Oracle's VirtualBox on Windows, Mac, and Linux
Windows and Linux Host
The right Ctrl key is the Host key on a Windows and Linux host
Mac Host
The left Command key is the Host key on a Mac host
GUI
The Host key is also presented in the lower right corner of the window running the VM:
This post covered what key is the Host Key in Oracle's VirtualBox on Windows, Mac, and Linux.
Reference
1.9.2. Capturing and Releasing Keyboard and Mouse in the Oracle® VM VirtualBox® User Manual at [link]