What does the prefix 'un-' signify when added to a word?

The prefix 'un-' signifies the meaning of "not" when it is added to a word. This prefix is used to create opposites or indicate negation. For example, when added to the word "happy," it transforms it into "unhappy," which means "not happy." This helps to convey that the quality or state described by the original word is being negated. Understanding prefixes like 'un-' is important as they can change the meaning of words significantly, allowing for richer and more precise expression in language.