What does WDF*IDF mean?

What does WDF*IDF mean?

The WDF*IDF analysis gives the following values

The maximum value and average value refers to the (usually 10) pages that rank on the first page of Google for the analyzed term.

The values text value and reference value refer to your own page.
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The text value indicates what text the search engine can find in the source text.
The reference value is the text that the user can see in the front end of the page.
​Text and reference value can differ because the user is often not shown everything in the frontend that was programmed in the source code.
The search engine only looks at the source code of the page that the value of the text value reflects.
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If the green line in the graph is centered between the orange and black lines, the word is used optimally on the page.
If the green line is close to the orange line or below the orange line, the word does not appear enough on the page. If the green line is close to or above the black curve, the word appears too often on the page. Google will interpret this as keyword spamming and penalize the page with a lower ranking.

For example, if the green curve is below the orange curve, then the word does not appear enough on your page.
To find out how often the word should be placed on the page so that the word is used perfectly on the page, enter the analyzed word in the text window.
The position of the green curve changes with each occurrence of the word. The word should appear in the text until the green curve is centered between the orange and black lines.

The value displayed is the resulting number that the word should be meaningfully placed in the text of the page.