RACI Assignment Matix

• Responsible (Those who do work to achieve the task, there can be multiple resources responsible).
• Accountable (The resource ultimately accountable for the completion of the task- there must be exactly one A specified for each task)
• Consulted (Those whose opinions are sought. 2 way communication)
• Informed (Those that are kept up-to-date on progress. 1 way communication)

Wikipedia has two entries for these:

• RACI diagram
• Responsibility assignment matrix