Here's a breakdown:
* Compound: A combination of two or more words.
* Adjective: A word that describes or modifies a noun.
Examples:
* "A state-of-the-art computer." (State-of-the-art modifies computer)
* "A two-day trip." (Two-day modifies trip)
* "A light-blue dress." (Light-blue modifies dress)
Important notes:
* Compound adjectives are usually hyphenated when they precede the noun they modify.
* When the compound adjective follows the noun, it is usually not hyphenated.
* Some compound adjectives are so common that they are no longer hyphenated (e.g., "high school").