The particleمَــا has many uses depending on the context. One of uses of مَــا is to ask a question. It’s literal translated word in the English language is “What”. Example is shown below…
What is your name ?
مَــا اِسْــمُــكَ ؟
What is this ?
مَــا هَــذا ؟
When preposition is preceded with مَــا, then ending alif (ا) gets drop as below…
بِ + مَــا = بِــمَ (with what ?)
لِ + مَــا = لِــمَ (for what, why ?)
مِــنْ + مَــا = مِــمَّ (from what ?)
عَـــنْ + مَــا = عَــمَّ (about what ?)