Please define the Candidate Source Values

Can you please define the meaning of the Candidate Source values?

Does Internal mean a Candidate that has been manually entered?
Does 'Imported by Parser" mean one that was Imported loaded through the Email tab?
Does "Resume Inbox" mean one that was Imported through RChilli?
Does "Embed" mean one that was entered through a web link?

If the field is blank because we didn't include it on the Application Form (Apply Now button), would the Source value be "Embed"??

thank you.