Caliph is the term for the Islamic leader of the Ummah, or community of Islam. It is an Anglicized/Latinized version of the Arabic word خليفة or Khalīfah, which means "successor", that is, successor to the Muhammad. Some Orientalists wrote the title as Khalîf. The Caliph has often been referred to as Ameer al-Mumineen (أمير المؤمنين), has been defunct since the abolition of the Ottoman Sultanate in 1924.
Ayatollah (Arabic: آية الله; Persian: آیتالله) is a high title given to major Shia clergymen. The word means 'sign of God', and those who carry the title are experts in Islamic studies such as jurisprudence, ethics, philosophy and mysticism, and usually teach in schools (hawza) of Islamic sciences. Ayatollahs can reach the position of a Marja-e-Taqlid, which allows them to issue fatāwi (Arabic, plural of "fatwa"). Also see The Grand Ayatollah.
Mullah or Mawlana
Mullah or Mawlana are Islamic clergy who have studied the Qur'an and the Hadith and are considered experts on related religious matters in this religion. The term Mullah is a variation of the word mawla(means master or lord) and Mawlana is its derivative (means my lord) and are used mainly in Central Asia and in the Sub-Continent .
Muezzin (the word is pronounced this way Turkish, Urdu, etc.; in Arabic: muathi (mu-a-thin) مؤذن [IPA: mʊʔæðːın) is any person at the mosque who makes the adhan, or athan (call to prayer) for the Friday prayer service and the five daily prayers, or Salah, Arabic for prayer. Some mosques have specific places for the adhan to be made from, such as a minaret or a designated area in the mosque. Major mosques usually have a person who is called the "servant of the mosque". He usually is the person who performs the athan. In the case of small mosques, the imam of the mosque would perform the athan (since small mosques may not be able to afford hiring a full time person as a mosque servant.
Sahib denotes an Islamic leader held in high regard by one or more other Muslims. The term is used almost exclusively in the sub-continent area. This Arabic word has different meanings, depending on the context, and can be translated as lord (or owner), companion, or friend.