Stay away from PR. As a rule of thumb, you don't get links from sites with genuinely high PR. Anything else is expensive and sometimes lethal. You can get penalised for buying PR. The quick answer is that a quality link is one which lasts. Look for established sites. But also look at their business model. What keeps them going? And if they are selling links without a no follow tag, be warned. They are not going to last.
Quality link is a link from a page having a strong popularity i.e good pagerank in the case of Google.
Quality back links are those links having good page rank, catche sites, unique content and relevant to your theme !
Quality is defined by the customers. Good quality link comes from good site with valuable contents and have high page rank stuff as well. Quality can be further boosted if it is relevant as well.
There are many factors, not only pr. Relevance and authority are the most important. In some niches, even some pr3 sites can rank at #1 on google. So if you are in one of those niches, get a link from that pr3 site is really valuable. And that link is quality link.
In other word no body knows, just keep building backlinks, so long as its not from spammy, pharma or adult sites (unless your site is an adult site) you should be ok
Lots of people know. They are just keeping to themselves because they are terrified everyone will trash the resources they use. This is what is so silly about it. Links are just links and every link counts. The value of the link lies in the anchor text you use and how long it lasts. Spammy links are low value because they don't last, not because they are spammy.
Relevant website, authority and high PR. Meaning, if you run arcade site and get backlink from FOG.com, it would boost your site up in a zillions of ways
Many people start with "traditional methods" to get links to your site, link exchanges and directories, and forget about the possibility of getting more valuable links to other websites writing.
Quality backlinks are those link which come from high PR sites and sites theme is related to ur site than google gives u benefits to ur site.
Quality links are those links that came from trusted sites, relevant sites, and sites that have high PR. If you have have backlinks from your niche market, that is quality.
Trusted sites are trusted for the very reason that they don't give out links. So that leaves us with sites that merely have high PR. But these don't come for free. One can only buy these sort of links and that has got to be the dumbest thing any web master ever does. You have got to look for sites which do offer links (without selling their links) and which have a reasonable chance of gaining, earning, that trust everyone talks about. Surely?
Quality link or backlink refers to those inbound-links that comes from "authority sites" for example sites which already have higher PR. I have wrtitten an in-depth article on it, check it out here if you want to know clearly