|(i) Unschooled and unacquainted with writing|
The majority of exegetes who favour this observation, have said that the word ummi is related to "umm" meaning "mother". The word "ummi" means a person who by birth is familiar with human written works and knowledge; or, it is related to "ummah" ie, who observes the customs of the majority, for the majority of people did not know about writing. Rather, only a few did. Likewise, the word " ummi" means, a man who is like the common people and ignorant. 
Some have said that the meaning of "ummah" is "creation", and "ummi" is one who has remained in his original state, ie, the illiteracy. For evidence one should refer to a poem  by Al-A'sha. However, be it either a derivation of "umm" or "ummah" - or whatever meaning of "ummah" is preferred - the meaning of the term ummi is the same, ie, "untaught".
(ii) An inhabitant of Umm al-Qura
Those who favour this view associate the word with "Umm al-Qura", ie, Makkah. The Qur'anic verse 92 of Surat Al-An am refers to Makkah as "Umm al-Qura": ...And that you may warn the (inhabitants of) Makkah and those (who live) around it (6:92). "
This possibility  has, since ancient times, found its way in the interpretive literature, and is confirmed in a number of Shi'ah ahadith, although these very ahadith have been found to be un-authentic and have been said to be of Israelite origin.  This possibility has, however, been rejected on the basis of certain proofs. 
One reason is that the word "Umm al-Qura" is not a proper noun, and has been applied to Makkah as a common attribute and not as a proper noun of Makkah. The word "Umm al-Qura" signifies the "centre of villages". Any point which serves as a centre of villages is known as "Umm al-Qura". From another Qur'anic verse, ie, verse 59 of the Surat Al-Qasas, it becomes clear that the word carries a descriptive rather than a nominative function: "Your Lord is not like this that He kills the residents of the villages until He sends a prophet to them in the centre of the villages, reciting to them Our revelations."
It becomes evident that in the Qur'anic language, any point constituting the centre of an area  is called its "Umm al-Qura". Moreover, this word "Ummi" used by the Holy Qur'an, has been applied to non-Makkans. Verse 19 of Surat Ali `Imran says:
"...And say to those who have been given the Book and the unlearned people (non-Jewish and non-Christian Arabs): `Do you submit yourselves?' ... (3:20)."
It then becomes evident that according to the custom of the time; and also in the language of the Holy Qur'an, all the Arabs who did not follow a heavenly book were referred to as "ummiyyin ".
More important still is the fact that this word "ummi" was applied for the common Jews who were not educated. Verse 78 of Surat Al-Baqarah of the Holy Qur'an reads: ' "Some children of Israil are "ummi"; who do not know their Book except false hopes... (2:78)".
It is obvious that the Jews whom the Holy Qur'an refers to as "ummi" were not the inhabitants of Makkah, but rather, most of them were residents of Madinah or of its neighbourhood. Thirdly, if a word is associated with "Umm al-Qura", literary rules require that "qurawi" should be said in place of "ummi", for, according to the lexical rules governing attribution, when modifying the modifier or the modified, particularly when the modifier is "ab=father", "umm=mother", "ibn=son'", or "bint=daughter", it modifies the modified and not the modifier, just as when modifying "Abu Talib", "Abu Hanifah", "Banu Tamim", they are referred to as "Talibi", "Hanafi" and "Tamimi".