define Long Tail

Definition:

Keyword phrases with at least three, sometimes four or five, words in them. These long tail keywords are usually highly specific and draw lower traffic than shorter, more competitive keyword phrases, which is why they are also cheaper. Oftentimes, long tail keywords, in aggregate, have good conversion ratios for the low number of click-throughs they generate.

How does the long tail applies to keywords? Long Tail keywords are more precise and specific, thus have a higher value.