Final answer:
A prefix is a word or group of letters placed before another word to modify its meaning.
Step-by-step explanation:
A prefix is a word or group of letters placed before another word to modify its meaning. It is an important part of the English language and can change the meaning of a word completely. For example, adding the prefix 'un-' to the word 'happy' creates the word 'unhappy', which means not happy.
Learn more about Definition of a prefix