What is the term for elements that are placed at the ends of words?

The term that refers to elements placed at the ends of words is "suffixes." Suffixes are a type of morpheme, which means they are the smallest units of meaning in a language. When added to the end of a base word, suffixes can modify the meaning or create a new word entirely. For example, adding the suffix "-ing" to the verb "run" forms the present participle "running."

In contrast, the other terms have different meanings. Affixes is a general term that includes both prefixes (which are added to the beginning of words) and suffixes. Prefixes, as mentioned, appear at the start of a word, such as "un-" in "undo." Circumfixes are a less common type of affix that attach to both the beginning and end of a word simultaneously, which is not applicable to the question about elements solely placed at the ends of words. Thus, suffixes are specifically the correct answer in this context.