Keyword density is a measurement of keyword means how much % of time you have used your keyword in between the content compared to the other no of words used in content.
Ex- If i have written 100 words in content and i have used my keyword 7 time in it then the keyword density is 7%.
Q-1 How much keyword density is preferable?
Ans – 5-7% keyword density is most preferable according to SEO Point of view.
Q-2 What happen if the keyword density exceed 7-8%?
Ans – If this happen then the site gets Google penalty for making over optimization of site.
Q-3 I am not able to put more keyword in my site due to less text so, Where can i place my keywords for exceeding my keyword density?
Ans – You can place your keyword in meta keyword, Description, Title, A tag of image which is used for image description, As a file name which is currently placed on site etc.
You can also ask your question about keyword density.