Here is your answer in both ethical and stuffed format
Ethical: Extensive usage of keywords in an irritating way (for the poor reader) in the hopes of getting better rankings is called as Keyword Stuffing, it is one of the age old (and used to this date) Black hat tick, that no longer works.
Stuffing: (Read it at your own risk)
"Keyword Stuffing is the process of stuffing keywords both long tail keywords and short tail keywords in a website's content (after researching keywords) in the hopes to get better ranking on Google for that specific keyword, keyword stuffing is wrong and Google has always said keyword stuffing will result in a website punished for the keywords that are used in keyword stuffing."