Adjectives 形 容词 xíng róng cí are words that describe nouns 名词 míng cí. Adjectives 形容词 xíng róng cí can be omitted (left out) from a sentence 句子 jù zi that contains the noun 名词 míng cí they describe. In other words, a sentence 句子 jù zi in English 英语 yīng yǔ is still proper (correct) if it does not contain an adjective 形 容词 xíng róng cí preceding (before) a noun 名词 míng cí. 
  

Examples of  proper sentences	Examples of  improper sentences
Basil is a smart boy.	Basil is a smart.
The dragon is a mythological creature.	The dragon is a mythological.

   
Interestingly, without the articles a, an and the in a sentence, the noun 名词 míng cí is not required after the adjective. For example,
 
Basil is smart.
  
Adjectives 形容词 xíng róng cí can be preceded by adverbs 副 词 fù cí which make them more descriptive. For example,
 
Basil is extremely smart.
  
See other parts of speech 词类 cí lèi. Click/Tab here.

Link to a Baidu video about adjectives 形容词 here.