In the Qur'an what does alif, lam, and meem mean?

These letters are one of the miracles of the Qur’an and none but Allah (Alone) knows their meanings. They are called Muqatta’at (dis joined or disconnected letters). 29 Surahs out of 114 Surahs have them in their beginning. The exact significance is unknown but Tafsir (Quranic exegesis) has interpreted them as names or qualities of Allah or content of the respective Surah.

In one interpretation, Alif-Laam-Meem means:

Alif = I am

Laam = An abbreviation of Allah

Meem = an abbreviation of Al-Aleem or the knowing

 

So in this case it means, I am Allah, the Knowing