It means that Allah is not similar to anything of the tangibles or intangibles, or the upper world (the heavens) or lower world (the earth and below it). Allah ta^ala said in Surat al-Ikhlas verse #4:
﴿ولم يكن له كُفُواً أحد﴾ سورة الإخلاص
This verse means: [Allah has no similar to Him in any way]. That is, there is nothing at all similar to Allah.
Imam Dhu-n-Nun al-Misriyy and Imam Ahmad said: “Whatever you imagine in your mind, Allah is different from it”. Imam at-Tahawiyy said in his book ‘Al-^Aqidah at-Tahawiyy’: “The one who attributes to Allah an attribute of mankind is a blasphemer.”