In SAP, maintenance planning plant represents the organizational unit where maintenance requirements for the operations / production system are planned. Maintenance planning plant is a plant in which maintenance tasks are planned and prepared.
In the PM planning plant, maintenance task lists are defined for the respective maintenance plants, spare parts planning is carried out on the basis of bills of material of the equipment, maintenance plans are managed and scheduled, maintenance notifications are created and maintenance orders are handled
You can define maintenace planning plant using the following menu path & transaction:
Enterprise Structure -> Definition -> Plant Maintenance -> Maintain maintenance planning plant