quality backlinks are organic links from reputable websites which are related to you.
eg, you make a site about business and the guy who owns business.com sees your site and thinks to himself, wow, I like that, so on his homepage he creates a link (Which you didnt pay for) and he says, yoursite.com is really good you must go and see it.
that is like a pr8 organic link from a website that is related.
Submitting articles or forum posting and link exchanges are all links you make for yourself. If that was what predominantly determined what search results were returned, the sites at the top would be the sites where the webmasters love themselves the most and have the time to create forum links etc.
Fact is, blogs, directories, and most of the websites that are in the footers of people posting in forums, have been created for the benefit of the webmaster/siteowner, made to generate traffic for the purpose of gleaning a few bucks from adwords etc. (EDIT: I SAY MOST NOT ALL, THERE ARE SOME REALLY HELPFUL SITES OUT THERE )
When people make a site worth using, something that has a benefit to people using it, the number of backlinks dwarf the number of backlinks that you could make for yourself.
take facebook for example, this is their backlink numbers for yahoo
79,200,000 Yahoo: 72,400,000
only a few thousand of those will be self created the rest will be organic, which is why it comes up in the serps before other peoples sites.
The fact that you can actually get in the serps by just creating back-links yourself is the reason that the net is flooded with 16-26 year old webmasters making blogs who have 0 skills in the topic they are talking about, and 0 programing, webmaster or business skills which is why they use out of the box programs, like adsense and blogspot etc.
However this flood of ignorance has its benefits, larger companies with bigger budgets are not comming into the online arena as fast as they could because of what the perceive as 'a lot of potential competition', what they dont realise is that the competition is just 17 year old uni students talking jibberish and that it is not a difficult task to shoot past them IF you take the time to make a different and beneficial to the user website.
If you want to get some decent info on SEO, just browse round, read the posts and make your own decision, dont ask questions, 3 months ago when I wanted to know something I made a post, and I have hundreds of people with less understanding than me, posting all sorts of BS trying to raise their own post count.
Also, take note, the net has a cyclic effect, 3 years ago it was myspace, then bebo, now facebook and youtube, come up with something that makes you a lot of money, withdraw that money and put it somewhere else, because no matter how fast you can come up with an idea, there are other people who can come up with betters ones faster and the value of your site will drop back down.
You-tube is worth a fraction of what it was because of face-book, and in 6 months, face-books value will drop as someone makes something better.
to answer your question, a quality link is a organic link from a reputable site, and anyone telling you different, doesnt have the creativity or patience to come up with something people will talk about without you paying them.
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