What is a Project Sponsor?
The sponsor is the person (or group) who provides the money and the political air cover, champions the project at the executive level, and formally authorizes it by signing the charter. The sponsor owns the business case; the PM owns delivering it.
The division of labor matters on the exam: issues within the project belong to the PM. Issues above the project — funding cuts, executive turf wars, go/no-go at stage gates — escalate to the sponsor. Running to the sponsor with problems you could solve yourself is the wrong answer; so is hiding a threat to the business case from them.
Worked example
When two department heads both refuse to release testers to a CRM rollout, the PM first negotiates directly. When that fails — it's an authority problem, not a scheduling one — she escalates to the sponsor, who settles it in one meeting. Right problem, right level.