The definition of a backlink according to Wikipedia:

A backlink for a given web resource is a link from some other website (the referrer) to that web resource (the referent).[1] A web resource may be (for example) a website, web page, or web directory... see here

In the world of Search Engine Ranking, backlinks are still important but the rules have changed a bit.  In order to get local rankings it is best to have links from other local websites that are located in the same city or state.  Using link farms may actually cause your website to be penalized so when ever possible you can build B2B links yourself by simply asking area businesses to do a trade. It is also helpbul to include a short paragraph or a "recommendation" to that business.  This page of links does not even have to linked to a menu on your website, it just needs to be included in the sitemap that is then submitted to the search engines.

It appears that content is king as Google gets better at understanding natural language. Also important is user traffic and engagement.  It does not appear that quality relevant backlinks will never become completely irrelevant but certainly junk irrelevant backlinks are becoming less and less valuable and even hurtful.   In the video, Matt Cutts takes on this user-submitted question: