The term "population density" refers to the concentration of individuals within a given area, often expressed as the number of individuals per unit area (e.g., per square kilometer). Population density can indicate how crowded a region is and influence factors such as resource availability, living conditions, and social dynamics. High population density can lead to competition for resources, while low density may result in isolation or underutilization of resources. It is a critical concept in ecology, sociology, and urban planning.