The term Sangha means an assembly or a community. Here again, two kinds of Sangha should be distinguished, namely, the Sāvaka-Sangha, or the community of (noble) disciples, and the Bhikkhu-Sangha, or the community of Bhikkhus or monks. The former is also called the Ariya-Sangha, or the Noble Sangha (community of Noble or Truly-Civilized Ones), while the latter is also named the Sammati-Sangha, or the conventional Sangha. The Noble Sangha of truly civilized people is formed of four types of persons, who are at four different stages of development, or levels of insight into the Truth. The Conventional Sangha of Bhikkhus, on the other hand, simply consists of four or more monks.
When Koṇḍañña gained the Eye of Truth, he became the first member of the Noble Sangha. When he was ordained a Bhikkhu, he became the first member of the Conventional Sangha. Thus, the event of the First Sermon marks the beginning both of the Noble Sangha of disciples and of the Conventional Sangha of monks.
The four types of persons who form the Noble Sangha are the Sotāpanna or Stream-Enterers (those who have entered the stream leading to Nibbāna), the Sakadāgāmi or Once-Returners (those who will return only once more to the vicissitudes of this world), the Anāgāmi or Non-Returners (those who will never come again to the dubious conditions of this world), and the Arahants or Worthy Ones (those who have achieved the ideal of perfection and attained to the goal of Nibbāna).
The Sotāpanna has achieved perfection in morality and has abandoned the three fetters of self-illusion, uncertainty and clinging to mere rules and ritual. The Sakadāgāmi has in addition mitigated lust, hatred and delusion. The Anāgāmi has achieved perfection in mental discipline and further eradicated the fetters of sensual lust and ill will. The Arahant has achieved perfection in wisdom and put an end to five more fetters, namely, attachment to fine-material existence, attachment to immaterial existence, conceit, restlessness and ignorance.