Sunnah mu'akkadah or "confirmed sunna" prayers, which Muhammad (ﷺ) "continuously performed and almost never abandoned" (according to tradition) ... Ghair mu'akkadah or "non-confirmed sunnas". These Muhammad (ﷺ) was not as fastidious in performing as he sometimes performed them "and sometimes abandoned" them.
Muakkadah and Ghair Maukkadah Prayers
Fajr: The first 2 rakaat of fajr prayers are Muakkadah, 2 rakaat farz
Zohr: First 4 rakaat sunnah Muakkadah, 4 rakaat farz, 2 rakaat sunnah muakkadah, 2 rakaat nafl
Asr: First 4 rakaat Ghair Muakkadah, 4 rakaat farz
Maghrib: First 3 rakaat farz, 2 rakaat Maukkadah, 2 rakaat nafl
Isha: First 4 rakaat Ghair Muakkadah, 4 rakaat farz, 2 rakaat sunnah Maukkadah, 2 rakaat nafl, 1 or 3 rakaat wajib and two rakaat nafl