A search engine penalty is an action taken against a website participating in deceptive or black hat SEO techniques.
Google’s definition of a "penalty" is some manual action taken against a site, opposed to the automated consequence of an algorithm or quality filter. Penalties can range from lowered rankings to complete blacklisting from the search engine's index.
A manual penalty can be issued by a search engine's web spam team if a website is discovered—through random manual review or spam report—using manipulative ranking tactics that go against any of the search engine's guidelines. Common penalties are speculated as being suppressed rankings of -30, -60, and -950 positions. Penalty duration is based on how badly Google's Webmaster Guidelines have been broken.
Manual penalties from Google are now almost always accompanied by email or notification from inside the website's associated Google Webmaster Tools account. Google issues manual penalties for practices such as:
To recover from a manual Google penalty, a reconsideration request can be made from Google Webmaster Tools once a website is free of manipulative tactics and bad practices that violate Webmaster Guidelines.
The automated algorithms that power search engine rankings are continuously evaluating web pages against various ranking signals. Google's ranking signals are always improving; therefore, a web page may lose its position in search results if its no longer meets the criteria of the core ranking algorithm. This is not a penalty, only a lack of signals that justify ranking above other sites.
Rankings lost to improved search engine algorithms are the easiest to recover from. Once necessary improvements are made, and the new web content is indexed, rankings will reflect the changes.
In addition to Google's core ranking algorithm are a number of algorithmic filters that are routinely run to remove spam and other types of low quality content from search results. Filters are not considered by Google to be penalties; instead they are said to be part of how they rank sites; just another ranking signal. As filters are designed to block content from search results, the're often seen as penalties. Filters such as the Panda and Penguin algorithms are activated periodically to clean the search results of:
Reinclusion requests don't help with Google's algorithmic or filter penalties. The only escape from penalties imposed by Google's automated quality filters are the removal of problem content or tactics, and time. Once the elements that triggered an automatic filter are removed, a site will be free to pass through to search results the next time that particular filter is refreshed.
It can take weeks or months for an algorithmic penalty to be lifted, as web page changes must first be re-crawled, re-indexed, and re-processed by the penalizing filter when it is updated.
To avoid search penalties altogether, stay within official Search Engine-approved Recommendations, and refrain from using search engine optimization techniques that don't offer clear benefits to human visitors as well.