The English language has the definite article “the”, which is used to refer to a specific object, person, or other noun. (the car, the books …) The indefinite article “a” or “an” is used in reference to a non-specific object or noun (a bicycle, a tree, …). In English, there is also the option of using no article, such as saying “I study chemistry“, instead of saying “I study the chemistry” or “I study a chemistry”.
Definite
In Arabic, the definite article is ال (al) and is attached in front of a word. For example, الموز (al mawz), the banana.
For words such as chemistry, the definite article should be used. For example, الكيمناء (al kiimiya’a).
Indefinite
For indefinite nouns, the ال article is omitted and you would simply say موز to say “a banana”. There is no indefinite article to use.