A bound morpheme is a word element that cannot stand alone as a word, including both prefixes and suffixes.
A bound morpheme is a morpheme (the smallest meaningful lexical item in a language). A morpheme is not a word. The difference between a morpheme and a word is that a morpheme sometimes does not stand alone, but a word on this definition always stands alone.
Free morphemes, by contrast, can stand alone as a word and cannot be broken down further into other word elements.
Attaching a bound morpheme to a free morpheme, such as by adding the prefix “re-” to the verb “start,” creates a new word or at least a new form of a word, in this case, “restart.”
Represented in sound and writing by word segments called morphs, bound morphemes can further be broken down into two categories, derivational and inflectional morphemes.
Hundreds of bound morphemes exist in the English language, creating near-infinite possibilities for expanding unbound morphemes—commonly referred to as words—by attaching these elements to preexisting words.
Nordquist, Richard. “Definition: Bound Morphemes.” ThoughtCo, Aug. 29, 2020, thoughtco.com/bound-morpheme-words-and-word-parts-1689177.