A near-Earth object (NEO) is an asteroid or comet that comes within 1.3 astronomical units of the Earth. This distance is roughly 120 million kilometers (75 million miles). NEOs are categorized into two main groups: asteroids, which are rocky bodies, and comets, which are icy bodies that release gas or dust. Scientists monitor NEOs to assess any potential threat they may pose to Earth. Some NEOs have orbits that bring them close to our planet, and understanding their paths helps in predicting future encounters. Programs like NASA's Planetary Defense Coordination Office work to track these objects and develop strategies for planetary defense.