The Typika is a service that is appointed by the Typikon on certain occassion, but that can also be conducted when a priest or bishop is not present. There are various modifications that are made to this service to incorporate elements from the Liturgy, some of which are designed to be led by laymen; and in some jurisdictions, it can also be a service led by a deacon, which includes the distrubution of Holy Communion. When held in a church, the doors of the iconostasis remain closed and the service is conducted in the nave.
Typika on days when there is no Liturgy, or only a Vesperal Liturgy
According to the Typikon, the Typika is appointed on those days when either there is no liturgy at all, or there is only a Vesperal Liturgy. The Typika follows the Ninth Hour and contains the typical Psalms and the Beautitudes that would otherwise have been done as part of the three antiphons of the Liturgy of the Catechumens. The text for this type of service can usually be found in the various Liturgicons and Horologions.
This Typika service is a specific form of service which mirrors the Divine Liturgy. It is used when a priest is not available or when a worshipper cannot get to a church. It is led by a deacon, subdeacon, reader, chanter, or the eldest experienced layperson present, in that order, unless a bishop or priest determines another leader.
This Typika service is a form of Pre-Sanctified Liturgy held by a deacon and authorized by the local bishop when a priest is unavailable. The deacon distributes communion to the faithful present at the service. It should be noted that while this service is blessed in some jurisdictions, it is not universally accepted, nor is it of ancient origin. However, the idea of deacons bringing communion to those unable to attend the Liturgy is an ancient custom, and so it can be argued that the ancient custom provides the basis for this more recent practice.