The meaning of al-huroof al-muqatta’ah in the Qur’aan
Question

                what is meant by the ayah Alim Lam Meem, and other similar ayahs in the quran? What have the scholars said regarding them?
Praise be to Allah. 
          A group of scholars, such as the Rightly-Guided Khaleefahs (may Allaah 
          be pleased with them), and others among the Sahaabah, Taabi’een and 
          their followers, refrained from interpreting this aayah and others which 
          contain al-huroof al-muqatta’ah [letters which appear at the beginning 
          of some soorahs]. It was not narrated that the Prophet 
          
          (peace and blessings of Allaah be upon him) interpreted them, so it 
          is preferable for us to say Allaah knows best what they mean. But it 
          was narrated that some of the mufassireen among the Sahaabah, Taabi’een 
          and their followers did interpret them, and they differed as to their 
          interpretation. 
 
          Al-Saheeh al-Masboor min al-Tafseer bi’l-Ma’thoor 
          by Dr Hikmat Basheer, vol 1, p. 94 
 
          Some of the scholars tried to discover the wisdom behind 
          these letters and said: These letters are mentioned – and Allaah knows 
          best – at the beginning of soorahs which point to the miraculous nature 
          of the Qur’aan, which implies that all mankind is unable to match it, 
          even though it is composed of the letters that they use in their daily 
          speech. This was the view supported by Shaykh al-Islam Ibn Taymiyah 
          (may Allaah have mercy on him) and was approved of by Abu’l-Hajjaaj 
          al-Mazzi (may Allaah have mercy on him). And Allaah is the Source of 
          strength. May Allaah bless our Prophet Muhammad and his family and companions, 
          and grant them peace. 
 
          Fataawa al-Lajnah al-Daa’imah, vol. 4, p. 144.