Definition: Defined as keyword phrases that typically do not have significant search volumes, these keywords also typically have very little competition. Generally speaking, the more words in a keyword phrase, the more likely it is to be a long tail keyword. These 'long tail keyword' are keywords that are used to find sites, though that are typically searched for so infrequently that they fall below the radar of popular terms and direct SEO efforts.

Long Tail Keywords in The Buying Process:
Though long tail keywords are searched for much less frequently that 'Head' type terms, long tail terms are far less competitive. Also, and most importantly, people search for long tail terms are further along in the buying process than those searching for generic 'head type' terms.
Case in point, consider someone searching for "widgets". Sure there are roughly 2 million searches a month for the term, but its very competitive, and costly to even attempt to rank for. Keep in mind there are millions of companies that sell pens. We can also surmize that many of the individuals searching for that term will be investigating the various types of pens available, looking for ballpoint pens, investigating the chemical properties of gel point pens, and the like. In fact, all will be early on in the buying cycle, at the information gathering /Determination of Alternatives Stage.
On the other hand, someone searching for a long tail term such as 'personalized ink pens' (1900 searches/month) already knows what they want. They're likely just looking for a few short list sites to determine where they will buy from. This is the other real benefit of long tail terms … people are very late in the purchase process, and are typically ready to buy!
How To Target Long Tail Keywords:
Ultimately, its simple. Add content. Add lots of relevant content. It doesn't have to be an ominous process, just a commitment to adding more valuable content relevant to your business each and every day.
Good video to explain the process!
Long Tail Keyword News Results:
Google: 20-25% of Queries Are New, and Never Seen Before – Its true … Google estimates roughly 20-25% of search queries have never been seen before.