Noon saakinah is a noon free from any vowel .  It remains unchanged in its written form and as well as in pronunciation when continuing to read after it and when stopping on it. Noon saakinah occurs in nouns and verbs in the middle of the word and at the end of the word, and occurs in prepositions and particles only at the end of the word.  The noon saakinah can have a sukoon on it, as in : , or can be written with no vowel on it, as in : .  Either way, it is considered a noon saakinah

The tanween is a term for an extra noon saakinah not used for emphasis, found at the end of nouns when continuing the reading, but absent from the noun in the written form (the noon of the tanween is pronounced but not written), and abandoned in pronunciation when stopping.  The tanween can be accompanying a fathah, a dhammah, or a kasrah, as in: . 

When there is a noon saakinah or tanween, we need to look at the next letter following the noon saakinah or tanween.  The letter that follows determines how the noon is pronounced, depending on the rule that is applied.  There are four rules of tajweed applied to the noon saakinah and tanween. The rules are applied to the noon saakinah in the same way that they are applied to the tanween.  The four rules are:

 The Making Clear : In this case the  is read clearly

The Merging : In this case the  is merged into the next letter either partially or completely.

The Changing :  Here the  is changed into another letter.

 The Hiding: The  is hidden so it is not a clear noon, but at the same time, not merged into the next letter.