Keywords are an important aspect to article marketing if you are seeking search engine traffic or organic traffic as a result of your article marketing efforts. After all you are seeking further exposure of your website through your article marketing efforts so the better your articles rank in the search engines result pages the better your potential for traffic from one effort. There is some debate in this area as there is in any internet marketing niche, but the same principles are always there, it is just whether or not each point is considered an actual positive or negativity to the article. By simple testing you will find what works best for your niche and your writing style.
What is a keyword?
This is simply what someone would type into a search function is their search for information. This is what you want to rank for to get that piece of traffic. It is a word you base your article around ( or a group of words) that tells the search engines this is what my article is about. Long tail keywords or those that are a phrase of 3-5 words are often easier to rank for, and may bring you more traffic then searching for number one with a whole army of competition against you.
Keyword density.
This is how often your keyword appears in the overall length of your article. A good guideline is 2% but instead of stressing over the actual density of your article, a way around it is to write conversationally. Write as though you were talking to a person informing them of the information instead. This way your article comes across naturally and in most instances you will have the keyword in your article at a perfect amount of times, without it looking forced or unnatural.
Keyword Stuffing.
If your article has 10%+ keyword density the spiders are going to look at it as spammy crap and disregard it. Search engines are built to understand the way people write and if you are just stuffing your keyword in, in unnatural ways, it won't help you. Search engines will see this as crap and you won't get the rankings you are hoping for. Write for your reader and you will do fine with the engines. After all you are writing to inform others as well as drive traffic to your site.