Hereunder are the different types of Salah.
1) Fardh is a first degree of obligation and is proven and indicative from a text that is explicit (قطعي الثبوت،قطعي الدلالة) for example, a verse of the Quran that is explicit on the issue, or Ahadith that are absolutely authentic (متواتر).
Ruling[i]: Leaving out a Fard act is sinful and punishable.
The Fardh Salah are: Fajr, Zohar, Asr, Magrib, Esha.
2) Wajib[ii] is a second degree of obligation after Fardh and is proven through such a text that is either explicit in establishing a point (قطعي الثبوت) and assumed by indication (ظني الدلالة) or vice versa.
Ruling: Leaving out a Wajid act is sinful and punishable.
Wajib Salah is Witr.
3) Sunnah Mua’kkadah[iii] is a third degree of obligation and is proven through emphasized actions of Rasulullah Sallallahu Alaihi wa Sallam.
Ruling[iv]: Leaving out a Sunnah Mua’kkadah act, is detestable and sinful.
They are[v]: 2 Rak’aats before the Fardh of Fajr, 4 Rak’aats before the Fardh of Zohar, 2 Rak’aats after the Fardh of Zohar, 2 Rak’aats after Magrib Salah, 2 Rak’aats after Esha Salah.
4) Sunnah-Ghair Mua’kkadah[vi] are those prayers which Rasulullah Sallallahu Alaihi wa Sallam did not perform continuously.
Ruling: [vii] If one practises on Sunnah Ghair Mua’kkadah, he will be rewarded. There is no sin in leaving out a Sunnah Ghair Mua’kkadah.
Sunnat-Ghair Mua’kkadah are:
4 Rak’aats before the Fardh of Asr, 4 Rak’aats before the Fardh of Esha.
5) Nafl[viii] are optional prayers Like Tahajjud Salah.
Ruling[ix]: If one practises on Nafl prayers he will be rewarded. There is no sin in leaving out a Nafl.
And Allah Ta’āla Knows Best
Source: Ask Imam