The term component refers to any specific element of the entirety of the project. Types of components can include specific schedule events, specific tasks, specific locations, and specific rules. Component is somewhat of an uber-term, in that it can refer to many different things within a project. Different team members may be assigned different components of a project, or within a project, to manage. Any one individual within a project team may have only one component to manage, or may have multiple components that he or she is responsible for. Components can, obviously be weighted in varied levels of importance. And as such, failure for one component to succeed may be little more than a nuisance, but failure of another component may be a catastrophic failure to the life of a project. As such, it is imperative that the most critical components of a project are determined at the outset, and if possible, the project team leader or project manager should assign his or her best team members to be responsible for those.
This term is defined in the 3rd edition of the PMBOK but not in the 4th.