Keyword stuffing is the number of times you mentioned the keyword phrase in your article, usually more than the required density. For example, if you are required to repeat the target keyword or phrase at 1v% or 2% density in a particular article, meaning for every one hundred words, you only mention one or two times for 2% density. If you repeat that more than the required density, you are keyword stuffingor spamming. Instead of gaining page-rank in the search engine, you will probably be penalized.