In my opinion Backlink quality is a concept that is not clearly defined. Backlink quality is backlink natural, useful to users and has many real clicks.
Backlinks from high authority pages linking to a relevant page with relevant anchor text looking very natural to the users are considered as quality backlinks.
When you make backlink (using targeted keyword or phrase in anchor text ) on a website which has good PA, DA and related your topic. It is called quality backlink.
Backlink in content
Backlink content is toxic
Backlink in the article with related content
Backlink has many links
High Pagerank
High PA
Dofollow backlink
Backlink brings a lot of traffic
Backlink has few links out
Backlink has many social interaction (Like, share, G +, Tweet ...)
Backlink tail GOV, EDU (Bonus)
and what can i do to get quality backlink
Quality backlinks refer to the links that are built using high quality content and from relevant domains and webpages.