Keyword stuffing is a somewhat antiquated term meant to describe the act of over saturating a web page with the targeted keyword in order to manipulate search engines for that keyword so that that particular web page appears atop the SERPs and receives all of the traffic.
What is Keyword Stuffing
It is considered to be a form of black hat SEO (see what is black hat SEO) because it works to manipulate or trick the search engines into ranking ones content higher through an unethical means. Instead of having to put in the work to come up with good content for the visitor to get ranked highly, the webmaster simply overuses their keyword to get the same effect.
A fundamental problem with keyword stuffing is that if it even works to help a web page to rank, the user experience is an afterthought so that that traffic is essentially worthless and wasted.
Keyword Stuffing Example
One keyword stuffing example would be to simply use a keyword an exaggerated number of times on a web page to the point where it looks suspect to the visitor themselves and makes for a lower quality experience.
Another keyword stuffing example which is much more unethical is to attempt to hide loaded keywords on a page by making the background color as well as the keywords themselves the same color so that they are not perceptible to the average website visitor.
This way the visitor is not offended by the gross repetition of that keyword but search engines will recognize the keyword on the page and will consequently rank that web page high.
Like most things, this technique of search engine manipulation worked for a period of time in the early days of the internet until it was exploited by an increasing number of webmasters over and over again.
The penalty today for keyword stuffing is that it simply doesn’t work as a ranking tactic and is consequently a waste of your time as you won’t see any traffic coming in due to it.
Related: What is the Optimal Keyword Density