Adjectives are the part of speech that modify, identify qualify or otherwise describe the noun.  An adjective is usually found immediately before the nouns that it is modifying.

The brilliant boy invented a cool online game.

The word brilliant is the adjective that describes the boy, a noun.  Cool and online are also adjectives as they describe game, a noun. Note that the adjectives are preceded  by words like the, a, an, etc.

Writers consider adjectives an enemy of good writing, as it is so easy to use a lot of adjectives to convey an atmosphere, but the result is tedious.  Mark Twain famously said:

“When you catch an adjective, kill it. No, I don’t mean utterly, but kill most of them–then the rest will be valuable. They weaken when they are close together. They give strength when they are far apart.”

Adjectives and Adverbs

The difference between adverbs and adjectives is that adverbs describe/modify everything that is NOT a noun or pronoun, while adjectives only describe/modify nouns and pronouns.

The big house was built on a hill.

Here is how an adverb looks in a sentence:

She walks slowly (slowly refers to the verb, walks)

He is incredibly handsome (modifies the adjective handsome)

Sometimes an adjective, used with certain nouns, follow the noun they are modifying:

I don’t visit downtown proper.

Degrees of Adjectives

Adjectives can express degrees of modification:

Sam is a fat cat, but Sparkle is fatter than Sam, and Ringo is the fattest of all our cats.

These degrees of comparison are known as the positive, the comparative, and the superlative. We use the comparative to compare two things, and the superlative is used when comparing three or more things.

An adjective is a part of speech that modifies or describes a noun, or which otherwise denotes its qualities