Project stakeholders are those who are directly or indirectly gets impacted positively or negatively by the project. So from the definition its clear that Stakeholder are almost everyone including project team to customer or even some other projects Project manager or a third party.
Managing everyone's expectation is challenging. So this knowledge area actually monitors or manages the involvement of stake holder their expectation or impact they can make on the project.
There are 4 processes in this area.
1 Identify Stakeholders
2 Plan Stakeholder Management
3 Manage Stakeholder Engagement
4 Control Stakeholder Engagement