The word UMMAH is an Arabic word which can be translated as “a nation” or “a community”. In the context of Islam, the word ummah is used to mean “the Community of the Believers”, and thus the whole Muslim world. 
It refers to two categories of people: The ummah of invitation (Ummah Al-Da‘wah) and the ummah of response(Ummah Al-Ijabah). The ummah of invitation includes all kinds of people, Muslims and non-Muslims. All of them are deserving of hearing the truth and of being invited to it. The other ummah, the ummah of response, is comprised only of Muslims.
Allah Almighty has sent his Prophetﷺto the ummah according to the first meaning, but Allah will only reward the ummah according to the second meaning – those who accepted the call of the Prophet (peace be upon him).
The term takes on religious connotations in the Qur’an where Allah (The God) is said to have sent to each ummah its own messenger. The messengers given special prominence as recipients of scripture. 
In fact, this word appears in the Qur’an with numerous meanings which can be summarized into five general categories as follows:
We find this meaning in the ayath: “Abraham was indeed a role-model (ummah), devoutly obedient to Allah, and true in faith.” [ Quran Sūrah al-Nahl: 120]
Ibn Mas`ūd turned to me and said: “Do you know what an ummah is. Do you know what it means to be devoutly obedient? I said: “Allah knows best.”
He said: “An ummah is someone who teaches people what is good. A devoutly obedient person is one who obeys Allah and His Messenger. This is Mu`ādh b. Jabal. He used to teach people what is good, and he used to obey Allah and His Messenger.”
We find this usage in the Qur’an in the ayath: “But the man who had been released, one of the two who had been in prison, and who now recalled after so long a space of time (ummah)...” [QuranSūrah Yūsuf: 45]
We find this usage again in: “And if We were to withhold the punishment from them until a stated period of time (ummah), they would certainly say: ‘What prevents it?’ Now surely on the day when it will come to them, it shall not be averted from them and that which they scoffed at shall beset them.” [QuranSūrah Hūd: 8]
We can discern a strong connection between the idea of an ummah as a nation and that of a specific historical timeframe, since a nation persists for a period of time and then comes to an end.
As Allah says: “To every nation (ummah) is a term appointed: when their term is reached, not an hour can they cause delay...” [QuranSūrah al-A`rāf: 34]
Allah says: “Nay! they say: We found our fathers on a path (ummah), and surely we are guided by their footsteps.” [QuranSūrah al-Zukhruf: 22-23]
Though they were clearly misguided, they were steadfast in their adherence to the ways of their forefathers. Therefore, this usage of the word ummah is appropriate here.
Allah says: “And when he arrived at the watering place in Madyan, he found there a group (ummah) of men watering their flocks...” [QuranSūrah al-Qasas: 23]
We also find: “Every time a new group (ummah) enters the Fire, it curses its sibling group that went before, until they all follow each other therein.” [QuranSūrah al-A`rāf: 38]
This is the usage that is most commonly found in the Qur’an, like where it says: “Humanity was a single community (ummah), and Allah sent Messengers with glad tidings and warnings...” [QuranSūrah al-Baqarah: 213]
Ibn `Abbās and others among the Companions and Successors relate to us that all humanity had at one time been united upon right guidance. For ten generations after the time of Adam(PBUH), humanity remained united in religious belief and were steadfast in monotheism. Then, devilish elements lured them from their faith, so Allah sent prophets to humanity to warn them and give them glad tidings.
We need to give this some thought. We know that even among Adam’s own children, there were those who were disobedient and sinful. We see this in the story of Cain and Abel. Indeed, humanity has been tried and tested ever since Adam and Hawwa(Peace be upon them) were sent out from Paradise. Therefore, it might be possible that the ayath stating humanity was united in faith refers to the state of the overwhelming majority of people during those first ten generations, and not to every single person. And Allah knows best.  
To every ummah (was sent) a Messenger: when their Messenger comes (before them), the matter will be judged between them with justice, and they will not be wronged. Quran Surah Yunus 10:47
Mankind was one single ummah. And Allah sent Messengers with glad tidings and warnings; and with them He sent the Book in truth, to judge between people in matters wherein they differed; but the People of the Book after the clear Signs came to them, did not differ among themselves, except through selfish contumacy. Allah by His Grace guided the Believers to the Truth, concerning what wherein they differed. For Allah guides whom He will to a path that is straight. Quran Surah Baqrah 2:213
If Allah so willed, He could make you all one Ummah: but He leaves straying whom He pleases, and He guides whom He pleases: but you shall certainly be called to account for all your actions. Quran Surah Nahl 16:93
Abu Hurairah (May Allah Be Pleased With Him) narrated that Messenger of Allah (Sallalahu alaihi wasallam) said: “Everyone of my Ummah will enter Jannah except those who refuse”.
“Who will refuse?”
He (Sallalahu alaihi wasallam) said,“Whoever obeys me, shall enter Jannah, and whosoever disobeys me has refused (to enter Jannah)”. Sahih Al-Bukhari Vol.9:7280
The Prophetﷺsaid: "My intercession is for my community." "My community will come forth bright and radiant." Muwatta Malik Book 15, Hadith 498 
Allah says: “You have been the best of communities brought forth for humankind: commanding good, forbidding evil, and believing in Allah.” [Quran Sūrah Āl `Imrān: 110]
What this ayath is saying is that this is the community (Ummah) wherein the best of humanity is to be found. They are those who are not concerned with themselves alone. They do not simply fulfil their own needs. They exist for all humanity, to teach them. guide them, and show them the way to Paradise.