A prefix is a set of letters that comes in front of a word to change its meaning. A suffix is a set of letters that is added to the end of a word.
An example of a word that contains a prefix is the word "unhappy." "Un" is added to the beginning of the word "happy" to change its meaning. An example of a suffix is the word "childish." The set of letters "ish" are added to the end of the word "child" to create a new meaning. A suffix often changes the class of word; for example, from noun to adjective or noun to verb.