A Permission to Officiate (PTO) is a concessionary ministry licence granted by an Anglican bishop.
A PTO is most commonly issued to a retired deacon, priest or lay reader over the age of 70 years. It allows the person to continue to perform the duties of their calling within the diocese (or part thereof, as may be specified in the license) for a limited period of time.
A cleric who was ordained priest or deacon by an overseas bishop needs to have permission to officiate from the archbishop of the province in which he or she intends to officiate before applying to the diocesan bishop for a diocesan licence or permission to officiate.
References
Permission to officiate Wikipedia(Text) CC BY-SA