Haram: forbidden, prohibited. It is necessary to abstain from the acts which are haram. If someone performs a haram act, he will be punished either by the Islamic court or in the hereafter or both.
Ihtiyat Wajib: precautionarily wajib. Its significance is the same as that of wajib with the difference that whenever a mujtahid says that "it is precautionarily obligatory," his followers have the option of leaving his taqlid (following) in that particular problem and following the fatwa of the second best mujtahid provided the latter has a different opinion.
Ja’iz, Halal, Mubah permitted, allowed, lawful, legal. The acts or things which are permitted and lawful. There no reward for performing it nor any punishment for neglecting it.
Marja' (pl. Maraji'): literally, it means the point of reference. It is used to describe the high ranking mujtahids who are a point of reference for the people.
Makruh: reprehensible, disliked, discouraged: It is used for the acts which are disliked but not haram. If one does a makruh act, he will not be punished; however, if he refrains from it, then he will be rewarded
Mujtahid or Faqih (pl. Fuqaha'): a jurist, a religious scholar who is an expert of Islamic laws, the shari'ah. Usually it is used for the high ranking mujtahids who are followed by the people.
Sunnat or Mustahab: recommended, desirable, better. It refers to the acts which are recommended but not wajib . If one neglects them, he will not be punished; however, if one performs them, he will be rewarded.
Wajib: obligatory, necessary, incumbent. An act which must be performed. One will be punished for neglecting a wajib act, e.g., the daily prayers.