[WHAT IS AN ADJECTIVE?]

ADJECTIVE is a word/ ADJECTIVES are class of words/ ADJECTIVE part of speech.

We will take it the first one ADJECTIVE is a word

:A word which qualifies(why noun is the way it is) a noun i.e. to say a word which describes quality of a noun. e.g. BIG BOY, LARGE SHIP, HUGE CAKE .

So, what are the adjectives in this case, BIG, LARGE, HUGE - are describing the quality or what the nouns (boy,ship,cake) look like.

Types of adjective: google definition:
possessive adjective   
proper adjective   
predicate adjective    
comparative adjective    
demonstrative adjective   
adjective phrase   
adjective clause   
predicative adjective   
attributive adjective