Secure Boot
Secure Boot usually refers to a platform firmware capability to verify the boot components and ensure that only your own operating system is allowed to boot.
Secure Boot has multiple implementations, the most well known one is UEFI Secure Boot, which relies on the UEFI platform firmware, but other implementations can exist on embedded systems.
On NixOS, Secure Boot can be enabled using the Lanzaboote or Limine projects.
It is recommended to set a BIOS password and enable full disc encryption to prevent attacks which can bypass Secure Boot.