A lustrum is a period of five years, often used in historical contexts to mark significant time intervals. The term originates from ancient Rome, where it referred to a purification ceremony held every five years to cleanse the city and its citizens. This ritual was important for maintaining the favor of the gods and ensuring the well-being of the community. In modern usage, "lustrum" can refer to any five-year period, especially in academic or organizational settings. For example, universities may celebrate a lustrum to commemorate milestones or achievements that occurred over the past five years, fostering a sense of continuity and progress within the institution.