I want to know that what is the difference between short tail keyword and long tail keyword. Which type of keyword is more effective for the promotion of website.
I'd answer both, but if you're just starting up, I suggest that you use a keyword that's a lot more specific, i.e. the long tails. Even though this doesn't bring you that much traffic, at least the chances of conversions are a lot higher because you're giving the people something that's close to, if not exactly, what they're looking for.
A long tail word consists of more than 2 words and it will give you bigger chances to appear on search engines.
The length of the term isn't as important as the frequency.
The long tail is a marketing theory that existed well before, and outside of, search but given the depth of search engines it's the prime example these days.
What it comes down to is that, while the top end of business is most visible, the bulk of activity actually comes from the less frequented, but far more volumous, individual. Basically while you see a lot of people searching for "pizza", if you add up all the people searching for pepperoni pizza or pizza delivery at disneyland you'd get a number that's far bigger than the bulk terms.
Draw this on a chart and what you get is a very short spike (the top term) and long but much lower quantity "tail". Because this tail goes so deep with all nuances that people input, it can mean big volume and better relevancy -- and quality trumps quantity any day.
As far as what's better, well as the longtail suggests, you'll get more volume from that. More so it's much easier to attack longtail terms than top ones. Of course the big terms remain the focus: it's appealing to go for the big wins and easier to focus on a few terms than thousands but even still you should avoid fixating on the top, the volume of the middle and bottom quartiles can be amazing and again there's that relevancy card.
Related reading: http://www.amazon.com/The-Long-Tail-Business-Selling/dp/1401302378
Many webmasters believe that through using long-tail keywords, the chances of conversions and sales will be going up considerably than the time they were only targeting keywords consisting of only a few terms that sometimes might not be even used by real customers. This theory is even accurate in advertising projects including AdWords because the longer phrases set by advertisers might be actually used by the real web shoppers.
When you target longer terms instead of one or two-word terms, you will be narrowing down the niches, naturally focusing on some web-specific subjects that can be great for many people to find. Besides, by turning to long-term phrases, especially for newly launched websites, getting top ranks seems more logical because the markets will not be that competitive as when you were only targeting very short, primary keywords.
Any word or term that is exact and generic is a short-tail keyword. For example, if your business is to sell cupcakes, your campaign's short-tail keyword must be "cupcake." When internet users search this term in search engine, your website or blog might appear in the front page. However, the use of short-tail keyword proves to be ineffective because the competition is tight and the chance of receiving unique clicks is low. A long-tail keyword is a group of words or terms that usually make sense. For example, if you're selling cupcake, your long-tail keyword to optimize must be "where to buy delicious cupcake" or "how to make a cheese cupcake."
When promoting a website, it's better to use a long-tail keyword for the reason that thousands of people around the world search it. Long-term keyword has also a high click rate and its competition is either low.
Short tail or simple keywords are composed of 1, or to the maximum of 3 words these keywords usually have high search volume this is the reason why these keywords have enough competition. On the other hand long tail keywords are usually composed of around 4 to 7 words. These keywords have less search volume and so less competition.
The core question here has been well answered [thanks to everyone who chimed in]... If there's another element you'd like to discuss please do so but let's avoid any further explanations of what's been covered.