NDM: Hafiz is an Urdu word as well. There are many Urdu words which have been taken from Arabic with similar meanings. Generally, Hafiz means protector or guardian in both Quranic Arabic and Urdu. ALLAH Hafiz is commonly known by all; whereas fi amaan ALLAH is understood only by a fixed group of people. It is said: Do not utter until or unless you yourself know what you are saying. I know most of people don't know the meaning of "fi" and then "amaan". Most often they use these words without understanding or if they understand the addressees usually don't understand. So, in short the words are not operative and do not move the feelings unless we understand them. A poem of Allama Iqbal can only be impressive for those who understand.

إِنْ كُلُّ نَفْسٍ لَمَّا عَلَيْهَا حَافِظٌ
There is no soul but has a protector over it.
Al-Qur'an, 086.004 (At-Tariq )

When we say "aap ka ALLAH Hafiz" – it means ALLAH (SWT) is yr protector. Or the responsibility of yr protection is given to ALLAH (SWT) – and almost every speaker as well as addressee knows and understands this.

It is our (Muslims') great misfortune that we read Quran again and again without understanding. On the other hand if we read English or Persian we know what we are speaking about. What will we tell others when we ourselves don't know about what we utter.

This is the greatest and foremost Sunnah to read Qur'an with understanding. Never Prophet (SAW) or his sahabahs recited like we do (recite) in India, Pakistan or Bangladesh. This is the basic reason that our lives are not changing. The importance of understanding can be judged from the following verse:

In Surah Hashr it is said:

لَوْ أَنْزَلْنَا هَذَا الْقُرْآنَ عَلَى جَبَلٍ لَرَأَيْتَهُ خَاشِعًا مُتَصَدِّعًا مِنْ خَشْيَةِ اللَّهِ وَتِلْكَ الأمْثَالُ نَضْرِبُهَا لِلنَّاسِ لَعَلَّهُمْ يَتَفَكَّرُونَ
Had We sent down this Qur'an on a mountain, verily, thou wouldst have seen it humble itself and cleave asunder for fear of Allah. Such are the similitudes which We propound to men, that they may reflect.
Al-Qur'an, 059.021 (Al-Hashr)
May ALLAH (SWT)increase us in our knowledge. Ameen!