In the different Zen Buddhist schools, there are specific ceremonies, or milestones in practice, through which a person formally expresses a commitment to follow the buddha way. These ceremonies differ from school to school, but overall, they follow a specific pattern. I am only intimately familiar with the Soto Zen Buddhism process, so here it is:
In Soto Zen Buddhism, there are three ceremonies by which a person formally assumes a specific place within the sangha: jukai, zaike tokudo, and shukke tokudo.
Jukai (Jap.) means "receiving the precepts." During this ceremony, a person expresses a commitment to live either according to the Five Original Precepts for Lay People or the Sixteen Bodhisattva Precepts. Those accepting the Five Precepts receive a wagesa, a strap-like garment worn around the neck; Those accepting the Sixteen Bodhisattva Precepts receive a rakusu , a bib-like garment also worn around the neck. In both ceremonies, a Buddhist name and lineage papers tracing the person's dharma heritage back to Shakyamuni Buddha can be given, but in some lineages this in only done if the person accepts the Sixteen Bodhisattva Precepts. Some practitioners go through the Jukai ceremony more than once.
Zaike Tokudo literally means "staying home to accomplish the way," and is sometimes referred to as "Lay Ordination." This ceremony is no longer recognized by the Soto Zen heirarchy in Japan, but is performed in the West. However, jukai and zaike tokudo are sometimes confused, however, and the same ceremony is called by one term or another, depending on where it's performed. Neither ceremony, however, confers any ecclesiastical (or clergy) standing on those completing it.
Shukke Tokudo literally means "leaving home to accomplish the way," and is also referred to as "Priest Ordination." During this ceremony the person also commits to living according to the Sixteen Bodhisattva Precepts and receives an Okesa (priest's robe) and lineage papers. After this ceremony, the person is a novice priest in an ecclesiastical (or clergy) system. The person then embarks on a period of training that hopefully culminates in Dharma Transmission, after which the person becomes a lineage holder capable of transmitting the lineage teaching as it was transmitted to her or him.