Hi Jayalakshmi,
Service Plan is a One Order Transaction which is basically used to for planning and performing recurring services of the objects. It is used as planning tool in the Service Planning Scenario so that the risk of unplanned downtime can be avoided. It helps in better management of Service Technicians, keep the backup ready in time of need.
Unlike any one order you can maintain, partner, organization, status, etc. Transaction Type data. Also you can create line Items and can maintain Item Categories as per your need.
You can check out the SAP Help for more information on Service Plan. You can perform a normal search on Service Plan in the SAP CRM Web UI to see the Service Plan templates.
Hope this helps.
Thanks,
Samantak Chatterjee.