What does it mean to lock or protect a note?

Here is a list of available actions on a note and what they represent:

Pin	Pinning a note will anchor it to the top of your list of notes, sorted according to the global sort order (specified in your Options).
Archive	Archiving a note will stash your note and hide it from your usual interface. Archived notes can be found by choosing the reserved Archived view in the tags panel. Archiving a note does not affect or improve performance, as the note is still saved and loaded, but not displayed in the list of all notes or within a particular tag. Archiving is useful for notes that no longer contain actionable data, but want to be preserved for historical purposes. For example, if a note contains a list of todos, and you've completed all the todos, archiving the note would make sense.
Lock	Locking a note will put it read-only mode, which means it can't be edited or deleted until you unlock it. This is to prevent accidental modification of sensitive notes, like passwords or credentials that aren't likely to change often.
Protect	Protecting a note marks the note as sensitive, and makes it so that additional authentication is required to view the note. The form of authentication used depends on your configuration. You will be asked to authenticate with your passcode or biometrics (mobile) if you have that configured. If you do not have a passcode or biometrics configured, you will be asked to authenticate with your account password. If neither of those are configured and there is no protection source available, the protected action will proceed without authentication. In addition, protecting a note will automatically hide its preview in your list of notes.
Preview	On web and desktop, selecting the Preview option will toggle whether to hide or show the note preview in the list of notes. You can hide previews for a particular note if you'd like to conserve vertical space in your list of notes, or to hide sensitive data. However, we recommend Protecting a note if you'd like to hide sensitive information.
Move to Trash	Moving a note to the trash will mark the note as deleted, and remove it from your interface. However, your note will still exist in your Trash, which you can access from your list of Views. From the trash, you can restore the note, or choose to delete it permanently. You can also empty the entirety of your trash by choosing Options → Empty Trash from the note editor panel.