I rather like the quoted Jill Whalen definition: SEO is about getting highly searched upon, highly relevant traffic that converts.
Of course most search queries are NOT a source of 'highly relevant traffic that converts'. Indeed, the SEs tell us that perhaps a quarter of every day's queries are a first instance - never before seen queries.
Which brings us to how we divide up and label search queries. And Barry Adams' State of Search referenced article Defining the Long Tail for SEO, also written today.
I take a much simpler but more complex approach that is both fluid and ultimately uncertain: in a given niche there are n-number of query terms (keyword/phrase). Each query term has certain traffic quantity and quality attributes. In it's simplest form: top 20% is the head (what Barry terms 'short tail'), rest (80%) is the tail (what Barry terms 'long tail').
Long tail traffic seems to have two characteristics:
1. It needs to be a fairly long keyword, at least 3 words or more.
2. It needs to be a low-volume keyword that doesn’t often get typed in to Google.
Personally I want to add a third characteristic to that, one that makes all the difference:
3. It needs to be a specific query fulfilling a specific informational requirement.
Most search demand curves tend to simplify and divide solely by quantity (search volume) without regard for the conversion quality. I view that as I did being /. or Dugg for those of you who endured those massive traffic spikes hoping for a few backlinks crumbs. Traffic for the sake of traffic. Blah.
Remember Jill's definition. SEO is about driving traffic for profit/revenue/conversion, browsing eyeballs bring up the rear. Head or tail defined by search volume only my a.s.s. As Barry observed:
Now, if one weights query term searches - not as per the web as a whole, but as per the site requirements - what is head and what is tail just might surprise you.
But the real money for this site is in the long tail. Take a keyword like ‘bosch avantixx wae24366′. The person who types that in to Google knows exactly what they’re looking for – a Bosch Avantixx washing machine, model number WAE24366.
Remember that going from the general (SE query volumes) to the specific (SE query value to a particular site) - especially as one is comparing apples and oranges (volume:value) is fraught with hazard. Yet that is exactly how many/most webdevs and SEOs work.
I think Barry summed up SEO and 'the tail' quite nicely:
Yes, sometimes it IS the presumed tail that wags the traffic. And the supposed head that brings up the rear.
...that is the real value of the long tail. It’s not about capturing all the possible traffic you can. No, it’s about capturing the traffic that is specifically looking for what you are selling.
And, finally, I really like Alan's descriptive text after the link to Barry's article:
Yup. The devil is in the details. And there are a lot of them.
...advocates why Long Tail should be part of your SEO regimen more clearly explains both why it’s valuable and that it’s not just about content, but about good Information Architecture, tags, breadcrumbs, and even taxonomy…