"Lost civilizations" refer to ancient societies that once thrived but eventually disappeared or declined, leaving behind intriguing ruins and artifacts. Examples include the Maya, known for their advanced knowledge of astronomy and impressive pyramids, and the Inca, who built a vast empire in the Andes mountains. These civilizations often vanished due to factors like environmental changes, warfare, or disease. Exploring lost civilizations helps us understand human history and the rise and fall of societies. Archaeologists study sites like Machu Picchu and Chichen Itza to uncover secrets about their cultures, technologies, and daily lives, revealing the complexities of human existence throughout time.