I only know about Keyword proximity. A phrase which can cover more then one "Unique" keyword in that is called Keyword proximity. For ex. we have site of tooth paste, we can use best healthy tooth paste. In that we covered Healthy Tooth paste and Best Tooth Paste. I think now you can understand it.
Keyword prominence means how prominent keywords are within a web page. Keyword proximity measures how close in the text the keywords are. Keyword proximity is applicable for keyword phrases that consist of 2 or more words.
Keyword prominence is the positioning of the keyword in the text.. If the keywords are used in the beginning of the sentences, then the keyword prominence would be high. Keyword proximity refers to how close two or more keywords are to each other.