YASIN, ALIF LAAM MEEM, HA MEEM AIN SEEN KAAF are all Huroof-e-Muqataat. Only Allah or His Prophet know the meaning of these haroof, but all these huroof are the most precious words for a muslim.
In the Name of Allah. O Allah, keep the shaytaan away from us and keep the shaytaan away from what You have blessed us with.
Note: *The Messenger of Allah [May the Peace and Blessings of Allah be upon him] said: whoever says this Dua and the wife was pregnant from that night, Shaytan will never be able to harm the child.