A root word is a basic word with no prefix or suffix added to it (a prefix is a string of letters that go at the start of a word; a suffix is a string of letters that go at the end of a word). By adding prefixes and suffixes to a root word can change its meaning.
A “root word” is the basic liguistic units of a word, the form of a word after all affixes are removed. Also known as the “stem word” -e.g. “export” has a root word “port”, sleepwalking has the root word “walk”. In many non-English languages, the root is formed of consonant sequences that do not represent an actual word.