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.

Web Design & Development Glossary
AJAX
asynchronous JavaScript and XML. A technique used in web page development.

Web Design & Development Glossary
API
application programming interface. A set of rules programs use to communicate with each other.

Web Design & Development Glossary
color stop
A special element that indicates a color to be added to a gradient.

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FTP
File Transfer Protocol. A network protocol useful for transferring files in a client-server relationship.

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HTML
HyperText Markup Language. The predominant language for building web pages.

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HTTP
HyperText Transfer Protocol. The primary networking language for the Internet.

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PHP
PHP Hypertext Processor. A scripting language that works well within HTML.

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socket
A technology that allows remote computers to maintain a persistent connection in order to communicate with each other.

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sprite
An graphic object on a web page that will be manipulated in real time.

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SQL
Structured Query Language. A programming language useful in managing relational databases.

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stateless protocol
An Internet procedure that completely breaks the connection between the client and the server after a transaction, meaning that the next transaction will require an entirely new connection.

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Telnet
A network protocol useful in interactive, text-oriented communications.

Web Design & Development Glossary
W3C
World Wide Web Consortium. The organization that sets international standards for the World Wide Web.