A note on Grammar: In Arabic, there are two types of letters that can follow the definite article: sun letters and moon letters.
Sun letters: We use our tongue and palette to double the sound of the [sun] letter that follows the definite article. In this case, we do not pronounce the ل in the definite article ال. It is called a liaison. Example: النّور. Remember that the doubling is sounds in Arabic is denoted by the shadda ( ّ).
Moon letters: We use our [lips] or throat instead to pronounce the ل fully in the definite article ال. These are called moon letters. Example: الخير.
In Arabic, if two nouns follow each other, one noun is indefinite and the second is definite, we need to add an ال to the second noun. This structure is called إضافة idafa. For example, صباح الخير, to mean morning of [the] good.
Listen to the following greetings and replies. Notice the definite article pronunciation.