Our scholars have divided Salat al-Nafl into two types.
1. Those which are recommended to be performed in a group [jama’a], such as the prayers of the two ‘Ids, the two Kusuf and Khusuf, the Istisqa’, and the Tarawih.
2. Those which are sufficient when performed indivdually [munfarid], such as the Rawatib, the Witr, the Duha, the Tahiyyat al-Masjid, the Istikhara, the prayers done in Mecca (Tawaf and Ihram), the Wudu’, the Awwabin between Maghrib and ‘Isha’, the Tasbih, the Tahajjud and the like.
All of the Nafila which are recommended to be performed in a jama’a are considered Mu’akkada [confirmed sunna], while all of the munfarid Nafila except for the Witr, a number of the Rawatibs, the Tahajjud, and the Duha, for example, are not Mu’akkada.
The Rawatib prayers (as they are originally called, “al-Sunan al-Ratiba ma’a al-fara’id”) are Nafila prayers that accompany the Fard prayers, whether offered before or after them. They are further divided into two types: the Rawatib Mu’akkada and the Rawatib Ghayr Mu’akkada.
>> More here