A project (or program) is any undertaking, carried out individually or collaboratively and possibly involving research or design, that is carefully planned (usually by a project team) to achieve a particular aim.
An alternative view sees a project managerially as a sequence of events: a "set of interrelated tasks to be executed over a fixed period and within certain cost and other limitations".
A project may be a temporary (rather than permanent) social system (work system), possibly constituted by teams (within or across organizations) to accomplish particular tasks under time constraints.
A project may be a part of wider programme management or an ad hoc structure.
Note that open-source software "projects" (for example) may lack defined team-membership, precise planning and time-limited durations.