What does the Arabic word ummah mean?

The word Ummah is used in the Qur'an and Sunnah with a number of different meanings. Sometimes when it is used it means a specified period of time: إِلَى أُمَّةٍ مَّعْدُودَةٍ Till a determined Ummah (term) This is also the meaning in the statement of Allah in Surah Yusuf: وَقَالَ الَّذِى نَجَا مِنْهُمَا وَادَّكَرَ بَعْدَ أُمَّةٍ Then the man who was released, now after Ummah (some time) remembered. [12:45] The word Ummah is also used to refer to the Imam (leader) who is followed: إِنَّ إِبْرَهِيمَ كَانَ أُمَّةً قَـنِتًا لِلَّهِ حَنِيفًا وَلَمْ يَكُ مِنَ الْمُشْرِكِينَ Verily, Ibrahim was an Ummah, obedient to Allah, Hanif, and he was not of those who were polytheists. [16:120] The word Ummah is also used to mean religion and religious creed. Allah mentions the polytheists said: إِنَّا وَجَدْنَآ ءَابَآءَنَا عَلَى أُمَّةٍ وَإِنَّا عَلَى ءَاثَـرِهِم مُّقْتَدُونَ Verily, we found our fathers following a certain way and religion, and we will indeed follow their footsteps. [43:23] The word Ummah is also used to mean a group (of people). وَلَمَّا وَرَدَ مَآءَ مَدْيَنَ وَجَدَ عَلَيْهِ أُمَّةً مِّنَ النَّاسِ يَسْقُونَ And when he arrived at the water (well) of Madyan, he found there a group of men watering (their flocks).[28:23] وَلَقَدْ بَعَثْنَا فِى كُلِّ أُمَّةٍ رَّسُولاً أَنِ اعْبُدُواْ اللَّهَ وَاجْتَنِبُواْ الْطَّـغُوتَ And verily, We have sent among every Ummah a Messenger (proclaiming): "Worship Allah (Alone), and avoid Taghut. [16:36] وَلِكُلِّ أُمَّةٍ رَّسُولٌ فَإِذَا جَآءَ رَسُولُهُمْ قُضِىَ بَيْنَهُمْ بِالْقِسْطِ وَهُمْ لاَ يُظْلَمُونَ And for every Ummah there is a Messenger; when their Messenger comes, the matter will be judged between them with justice, and they will not be wronged. [10:47] The meaning of Ummah here is the nation who has had a Messenger to them, including believers and disbelievers among them.