Fard, Wajib, Mustahab, Nafl (فرض، واجب ،مستحب، سنت موکدہ، غیر موکدہ)
1 ) Fard ( also called wajib ) refer to things which are required and we will be held accountable for ignoring them. This should not be confused with Wajib in Hanfi Epistemology which is a separate thing in their jurisprudence. 2) Mustahab ( recommended ) refer to those acts which are not fard but Muslims are encouraged to do. Some Mustahab acts are strongly emphasized like some sunnah acts like circumcision, eating with right hand etc. or some Nafl Salah ( also called Sunnat-e-Mokada ). 3 ) Nafl refer to things which are not required, however they will be rewarded if done like some Nafl Salah not emphasized ( also called Sunnat-e-Ghair Mokada ). In broad terms, when someone commits an act prohibited in Quran (i.e. declared Haram ) or ignores any obligatory part of religion (i.e. Fard ), then it will result in a major sin . AND Violation of all matters of etiquettes , recommended acts in religion or adoption of discouraged acts which are transmitted through Quran and Sunnah , if intentional, would result in minor sins . For example, if one intentionally eats with his left hand despite being right handed. For a detailed study , please refer to the following threads : Discussion 80980 Discussion 71403