The practical laws of Islam that are related to the actions that one must perform and those that must be avoided, and are the responsibility of everyone to learn, are called the Ahkam(rules).
Every action that a person performs has a specific ruling in Islam. The various actions that we perform, which are related to our responsibility (to Allah) are divided into five categories: Wajib, Haram, Mustahab, Makruh, and Mubah.
Wajib: Those actions that must be performed, and turning away from them, incur Allah’s punishment – for example Salat, and Sawm.
Haram: Those actions which must be avoided, and performing them incur punishment from Allah, like lying and oppression.
Mustahab: These are actions which are recommended to be performed and earn the person a reward, but not performing such actions do not incur punishment from Allah – for example saying Salam and giving Sadaqa.
Makruh: Those actions which are better if not performed, and if avoided, earn a reward, but if performed, do not accompany a punishment – for example, sleeping in a Masjid, and the praising of goods that a person sells (otherwise known as advertising).
Mubah: Those actions whose performance or turning away from are equal; meaning one neither gets are ward, nor punishment – for example walking or sitting.