TFIDF stands for “Term Frequency, Inverse Document Frequency”
Today keyword use is a much more refined process. It is commonly believed by many a SEO expert that the “TFIDF” model is employed to determine keyword function in a data set. TFIDF stands for “Term Frequency, Inverse Document Frequency” This is an equation that sets sort of a golden ratio of using keyterms on your website.
What TDIDF means
What TDIDF means is that first you have to have a keyword on your site if you want to be in the database. You have to use the key term in several areas to attain a level of “Term frequency” (i.e. Title, Header, ALT attributes, content). Now, the Inverse Document Frequency is factored in to factor out commonly used terms in multiple string searches. Words like “The” , or other key terms that are essentially very prevalent on the web pages. Inverse Document Frequency takes all the documents in a file, i.e. your website, and factors the term frequency for the entire set of terms in the document file. This means that keywords that are used somewhat throughout the document set will be of significance but that there is a thresh hold that can be crossed to making those signifigant key terms appear to be common dialogue.
How many keywords and where?
Therefore, I suggest using your key terms that you are ranking for on your home page or landing page; then mix up the keyword use in the titles, headers, descriptions, etc. etc. in the rest of the document files so that you are not using your key terms in more that half of those files. Instead of overusing your key terms that you are trying to rank for use the surrounding similar terms that relate to what your main search term is.