An affix is a morpheme added to the beginning or end of a word to change its meaning or function. There are two main types of affixes: prefixes, which are added to the beginning of a word, and suffixes, which are added to the end. Common examples of prefixes include re-, un-, and multi- while common suffixes include -ly, -ness, -ion, and -er or -or. Affixes can change a word from one part of speech to another, such as making an adjective into an adverb with the -ly suffix.