Planning fundamentals
Media plan
A media plan is the document or system that records a campaign's allocation decisions: audiences, channels, platforms, tactics, budgets, flighting, KPIs and rationale. A working plan continues after launch as the baseline for comparing planned with actual delivery.
In practice
Each line of a good plan represents a decision that can be activated, paced and measured independently. 'Paid social' is too broad; 'Meta prospecting against persona A' is a usable planning line.
The most common failure is a plan built for approval that dies at launch, leaving actual spend tracked in a separate file. Keeping plan and actuals on the same object is what turns a document into a control system.