There is some difference concerning the meaning of the word alamin. It is the plural of alam which is itself a plural – it has no singular. Al-Fara and Abu Ubaydah said, ‘al-alam is a term referring to anything that possesses an intellect and these fall into four categories: mankind, jinn, angels and satans. The term alam does not refer to the animal kingdom because this plural refers to those who possess an intellect specifically.’
It is also said that it refers to every race or species of creation and to each generation of that race as stated by Qatadah and at-Tabari. Therefore mankind is an alam and likewise every individual race amongst them would be an alam also, just as each generation of the race would be an alam. Similarly the Jinn are an alam etc.
Some of the scholars stated that al-alam is derived from al-allamah or sign because the existence of the world is a sign, without doubt, of the existence of its Creator who is described with perfect and magnificent Attributes. Allah, Exalted is He said, “Indeed in the creation of the heavens and the earth and the change of the night and day are signs (ayat) for the people of understanding.” (Ali Imran 3:190) and in the language ayah means allamah. (al-Baghawi, vol 1, p52)
However in another place in the Qur’an, Allah Himself has indicated its meaning, “Pharaoh said: and what is the Lord of the alamin? He (Moses) said: the Lord of the heavens and the earth and what is between them.” (ash-Shu’ara 26:23-24) and therefore the most correct view is that it refers to all that is in existence besides Allah. (ibn Atiyyah, vol 1, p67)
Qatadah said, ‘Al-alamun is the plural of alam and it refers to everything in existence besides Allah.’
Ibn Abbas, may Allah be pleased with him, said in explanation to this verse of al-Fatihah, “All praise and thanks are due to Allah, to whom belongs the creation in its entirety, the heavens and the earth and whosoever is in them and whatsoever is between them – that which is known and unknown.” (at-Tabari, vol 1, p92)
The Spiritual Cure: An Explanation of Surah Al-Fatihah prepared and translated by Abu Rumaysah Pages 82-84