What is keyword density? Is keyword density even a factor is SEO?

[SEO.Ninja]

Hi,
Keyword density is a measure of the relative importance of a keyword on a given page, based on its rate of occurrence.
Keyword density deals with the ratio of your keywords in light of the total number of indexable word placed in your webpage.

For Example:
You have 100 words article then having a 1% Keyword ratio means that you should have the presence of your keyword one time within that 100 word text.
Keyword density is not same for all search engine.
Google recommended keyword density range from 1% to 2%.