Morphology is the study of forms. A morpheme is the smallest unit of meaning in a word. In the word "reopened", there are 3 morphemes: "re" meaning again, "open" meaning the opposite of close, and "ed" being a grammatical suffix indicating past tense. Similarly, the word "tourists" contains 3 morphemes: "tour" meaning travel, "ist" meaning a person, and "s" indicating a plural form. Morphemes can be free, able to stand alone as a word carrying meaning, or bound, unable to stand alone and instead modifying the meaning of other morphemes by being added as a prefix or suffix.