Hi DL_2016,
Thanks for your reply.
I have summarized your questions, here are my replies to them, which may benefit other community members.
1. What is Delve?
Delve helps you discover the information that's likely to be most interesting to you right now across Office 365. Find information about people, which can help others find you. For more detailed information about Delve, this article is for your reference: What is Office Delve?
2. Do Discover view items come from anywhere else other than OneDrive or SP online?
Delve shows you a mix of content from across Office 365. You’ll see both your own documents, and documents your colleagues are working on. These are documents that are stored in OneDrive for Business or SharePoint in Office 365, or that have been shared with you as attachments in emails. Webpages that have been posted to Yammer, can also show up in Delve. The article you provided is quite useful to refer to: How does Office Delve know what's relevant to me?
Regards,
Yoga