An adjective is a word which describes or limits a substantive.
This it usually does by indicating some quality.
An adjective is said to belong to the substantive which it describes or limits.
An adjective limits a substantive by restricting the range of its meaning.
The noun box, for example, includes a great variety of objects. If we say wooden box, we exclude boxes of metal, of paper, etc. If we use a second adjective (small) and a third (square), we limit the size and the shape of the box.
Most adjectives (like wooden, square and small) describe as well as limit. Such words are called descriptive adjectives.
We may, however, limit the noun box to a single specimen by means of the adjective this or that or the, which does not describe, but simply points out, or designates. Such words are called definitive adjectives.