Difference between keyword density, frequency, prominence and proximity, and how they affect search engine rankings?
Keyword density & frequency are very similar - The number/percentage of times any keyword or a phrase appears on a webpage. Keyword prominence - Basically out of all the keywords, the most prominently listed keyword. Keyword proximity - The distance between two repeating keywords. Appropriately using all of the above have a good effect on the rankings. Overdoing the same can result in spamming. Using keywords in appropriate combination or words in page titles, headers and contents can help you in a much better SEO campaign.
To expand on prominence - I would add that this term also refers to the importance of the tags your keywords are in. For instance does the keyword appear in your title? does it appear in your domain? does it appear in your h1 tags? All these things add to your keyword's prominence in the eyes of the search engine.
Think of it in terms of relevance. If you were Google and a person searched for "Battle of Hastings" the more prominent the words are on the page the more relevant that page is for that search term. Use in title, H1, at the beginning of the doc, at the end and with synonyms throughout signify more relevance. Greater prominence = great importance and relevance. Write for people. Not engines!