Minyan מניין
Ten adult men, without whom the kaddish is not said, the Torah is not read and the words of sanctification are not spoken. The number by which it is measured whether there is a community in this place.
One may pray alone. But there are things said only "in sanctity": the kaddish, barchu, kedushah, the reading of the Torah from a scroll, the seven blessings for a bridegroom. For these, ten are needed, and this is not a round number but a derivation: the word "congregation" is learned from the account of the ten spies who brought back an evil report.
What this arranged. The whole settlement of the people. A Jew could not settle where ten could not be gathered—or rather he could, but lost the service. So people settled close together; so agreements about moving stipulated the presence of a minyan; so a rich merchant living apart maintained ten men about him. The minyan is the smallest unit of Jewish geography.
Who counts. Men from the age of thirteen. The argument over whether women are counted is a modern one, and it runs along the same line by which the denominations parted in the nineteenth century; orthodox communities count as before. We name the argument, we do not settle it.
And about nine. There is an old bitter saying: where there are nine, they are waiting for the tenth. In communities dwindling through departures, the last minyan is a date that gets written down: with it the community ends.
On the timeline
Related
Sources
Chazal: Mishnah, Talmud, midrash, Zohar
- Mishnah Megillah 4:3 and Megillah 23b — the list of what is done with not fewer than ten, and whence the number is derived
- Berachot 6a — where ten pray, the Divine Presence is there
Basis: Talmud and midrash.