An "era" is a significant period in history characterized by particular events, developments, or cultural trends. For example, the Victorian Era in the 19th century was marked by the reign of Queen Victoria and notable advancements in industry and culture. Each era helps us understand how societies evolve over time. Eras can also refer to geological time, where the Earth is divided into different periods based on major changes in the planet's history. The Mesozoic Era, for instance, is known as the age of dinosaurs, showcasing how life on Earth has transformed through various ages. Understanding eras helps us grasp the timeline of human and natural history.