Keyword Stacking and Stuffing
Keyword stacking and stuffing is one of the crudest ways to try to cheat your way through search engine optimization. You may run across web pages that contain the same word or term, or maybe several words or terms, repeated again and again, often in hidden areas of the page (such as the KEYWORDS tag), though also sometimes visible to visitors.
Search engines have been aware of keyword stacking and stuffing for years and are pretty good at finding these days. It’s rare to find crudely keyword-stacked pages ranking well in the search results anymore.
The web designer has repeated the word glucosamine numerous times in the following figure, each one in a hyperlink to give it a little extra oomph. This page was found in Google a few years ago by searching for the term glucosamine glucosamine glucosamine; more recently, the same search phrase didn’t pull up anything nearly as crude as this page.
Look at this tactic from the search engine's perspective. Repeating the word glucosamine over and over isn't of any use to a site visitor, so it's understandable why search engine designers don't appreciate this kind of thing. This sort of trick rarely works these days, so sites doing this are also becoming less abundant.
The terms keyword stacking and keyword stuffing are often used interchangeably, though some people regard keyword stuffing as something a little different — placing inappropriate keywords inside image ALT attributes and in hidden layers.