Definiteness
By default, a noun is indefinite. There is no article, sign, or any mechanism that indicates this. In order to make a noun definite, one of seven things must be done. In other words, there are seven ways in which a noun is made definite; if none of those have been used, the noun is indefinite.
The methods of definiteness are as follow
1. the noun is a personal pronoun (“هو”)
2. the noun is a demonstrative pronoun (“هذا”)
3. the noun is a relative pronoun (“الذي”)
4. 4. the noun is a proper noun (“Saudi Arabia”)
5. it is prefixed with the definite article الـ
6. it is a non-final noun in a possessive structure and the final noun is definite
7. the noun comes after a particle of vocation (“يا رجل”)