Let us take the following scenario:
“Government came up with a sea canal project last year. Currently, ships have to travel around an island to reach other side. By executing this project, ship travel becomes cheaper as it takes shorter route than earlier.
But environmentalists are concerned that this project will endanger the fragile marine ecology of the area through constant dredging to maintain a canal depth of about 10 m. The increase in shipping traffic will inevitably result in an increase in oil spills and marine pollution. So they protested for the execution of the project without proper clearance from national environment group before starting the project.”
What do we understand from this story?
Environmental groups are negative stakeholders in the sea canal project as they stops the project execution.
Let us examine the definition of Project stakeholders now.
Project stakeholders are individuals and organizations that are actively involved in the project, or whose interests may be affected as a result of project execution or project completion.
They may also exert influence over the project’s objectives and outcomes.
The project management team must identify the stakeholders, determine their requirements and expectations, and, to the extent possible, manage their influence in relation to the requirements to ensure a successful project.
As mentioned in the example, it is not required that stakeholders must have negative influence on the project. Stakeholders may have a positive or negative influence on a project.
So, what is positive or negative stakeholder means?
Positive stakeholders are those who would normally benefit from a successful outcome from the project, while negative stakeholders are those who see negative outcomes from the project’s success. 
It is Project manager’s duty to identify all stakeholders, gather their requirements, manage their expectations and appropriately communicating them in timely manner depending on their responsibility & authority levels. Moreover, project stakeholders have high influence over the project at the start and it decreases as the project continues.
Let us examine few key stakeholders:
• Project manager – The person responsible for managing the project.
• Customer/user – The person or organization that will use the project’s product.
• Performing organization – The enterprise whose employees are most directly involved in doing the work of the project.
• Project team members – The group that is performing the work of the project.
• Project management team – The members of the project team who are directly involved in project management activities.
• Sponsor – The person or group that provides the financial resources, in cash or in kind, for the project.
• Influencers – People or groups that are not directly related to the acquisition or use of the project’s product, but due to an individual’s position in the customer organization or performing organization, can influence, positively or negatively, the course of the project.
The list is just a gist of key stakeholders. But whole list differs from project to project even projects are executed within the same organization.
. PMBOK® Guide – 3rd edition – Page #. 24
. PMBOK® Guide – 3rd edition – Page #. 25
. PMBOK® Guide – 3rd edition – Page #. 26