The adjective modifier integral refers specifically to a number of project management components that are essential for the proper progression of the project from one state to the next. Integral can refer specifically to any element within the project that it is determined to be essential to the overall and total completeness of said project, requisite to the proper functioning within the project and to the proper advancement of the project team from one phase to the next; in cohesion with an elemental constituency with the project; or formed as part of another reliant and dependent unit with another element of the said project. There may be a very long and lengthy list of integral components within a particular activity, or there may be only a very select grouping of such elements, and this is typically something that is determined at a very early phase of the project planning process.
This term is defined in the 3rd edition of the PMBOK but not in the 4th.