In general, the term "Arab" in modern times is applied to a large group of different peoples that share in common the Arabic language, which for the overwhelming majority of them is not their original one but the tongue imposed to their forefathers by the Arabian conquerors. Such a definition is ethnically unsuitable, in the same way as it would be inappropriate to call "Spaniards" to all Spanish-speaking peoples or "English" to all those non-British folks whose primary language is English. It is true that the Arab countries have not only language in common but also most cultural features as well, yet, this is the result of the colonization and subsequent annihilation of the original pre-Arabic culture. Therefore, it is more correct to speak of them as "Arabized" peoples rather than Arabs.
From the ethnic viewpoint, the term "Arab" is roughly equivalent to "Arabian", namely, in reference to the only people considered to be Arab since the beginning and identified as such by themselves and by their neighbours.
It happens frequently that the word Arab is misused on purpose for political strategy: 1) by applying this term as an ethnic definition to the Arabized peoples (mainly North-Africans), in order to increase the number of the Arab population, and 2) in a quite improper way, by calling "Arab" to ancient peoples that existed in the Middle East in order to claim historic rights and legitimate the Arab occupation. So, it is necessary to reach a clear definition in two directions: which peoples are Arabs and which are not. Concerning the origin, the most widespread myth is that Arabs are Ishmaelites, what in the case of all the Arabized peoples is not true at all, and regarding Arabians is only partially true.
The original Arab culture has been lost and the most reliable information we have about it comes from external sources, because Islamic revisionism has produced a legendary account in replacement of the scientific truth, and so one of the most fascinating cultures of the past is now missing.
The Arabian myths have been created in order to legitimate the "pre-existence" of Islam by ascribing fanciful tales allegedly happened in Arabia to Hebrew Patriarchs and Prophets. Through these legends turned into "history", Arabs claim an Avrahamic origin through Yishmael, who was only the forefather of some tribes that intermarried with many other peoples that were already settled in Arabia much earlier than him and within which the Ishmaelite lineage was largely assimilated. Therefore, the equation Arab = Ishmaelite is a myth, because Ishmael was not an Arab, nor the forefather of all Arabs; actually, his descent contributed to the formation of the peoples that came to be known as Arabs some centuries later. Connected with the alleged Ishmaelite identification, the Semitic identity is taken for granted, yet, this is also a half-truth because the Arabian ethnicity and culture arose from an original Kushite stock that was subsequently assimilated by the Semitic tribes that came after them, and even the Ishmaelites were a mixed group with a strong Hamitic component, as we will see in this essay.