A Summary Level Planning Package (SLPP) is an aggregation of work for far-term efforts, not able to be identified at the Control Account (CA) level, which can be assigned to reporting level Work Breakdown Structure (WBS) elements (and is therefore not “Undistributed Budget”). 
SLPP are used to establish high level holding accounts for budget authority that is identified to some work scope, but which, for business reasons, has not yet been allocated to control accounts. A difference of the SLPP, when compared to Management Reserve or undistributed budget, is that the summary level planning package budget is identified to specific work scope and it is time-phased for interim resource planning. 
ANSI/EIA 748 – Guideline 8
Budgets for far off work can be held in levels above the control account level in Summary Level Planning Packages (SLPPs). In some instances, over-target-baselines (OTBs) may be used if approved by the customer.
AcqLinks and References:
- Defense Acquisition Guidebook (DAG) – Chapter 3.4
- DoD Earned Value Management Implementation Guide (EVMIG)