In this case, it's Boot0008, which I snipped but which identifies a USB flash drive - you booted using the fallback boot loader stored on that drive. The BootCurrent line identifies the entry that was used to boot the computer.
The remaining entries follow these patterns. If you're having a boot problem, I recommend you ask another question and provide details. Your example may have been missing an Ubuntu entry because you haven't yet installed Ubuntu, because you installed Ubuntu in BIOS/CSM/legacy mode (a mistake), because your EFI is buggy and so efibootmgr was unable to add an entry, or because you explicitly deleted the entry once it was created.
Here's such an entry from one of my computers: Boot000D* ubuntu HD(1,800,112800,a8d39218-44ce-455b-8735-919754df131d)File(\EFI\UBUNTU\GRUBX64.EFI).BOĪs you can see, that's pretty similar in basic form to the entry for the Windows boot loader, although of course the details differ. Notably absent from your list was an entry for booting Ubuntu. OTOH, sometimes you'll see other options, like entries that refer to BIOS-mode boots. Many EFIs produce much shorter lists - for instance, they may be missing the built-in options or the options for PXE-booting from the network. The Windows entry includes more gibberish-like data at the end, but in this case it's a UTF-16 string that's passed to the boot loader as an option. Both entries include a filename ( File(.)).
The latter includes a GUID for the partition, along with some other idenfications. They do so with slightly different syntaxes - note that the first begins with ACPI(.) and PCI(.) entries, as earlier ones did, whereas the second uses an HD(.) identifier. These entries both identify EFI boot loaders stored on the hard disk.