Those with the highest search demand are called head terms.
Conversely, those with a relatively low demand are considered long-
tail.
Why?
When you graph them out, head terms fall off quickly in terms of the
total number of keywords, whereas lesser searched terms seem to
go on forever like a tail.
The middle of the graph is often aptly named “middle” or “chunky
middle” (or torso).
With 15% of searches being new to Google each day, it shouldn’t be
surprising that most search queries are considered long-tail, even if
each individual long-tail query gets searched very few times.
Head vs. Long-Tail Keywords
WHY KEYWORDS ARE STILL SO VERY IMPORTANT FOR SEO