Visit CNEOS (the Center for Near-Earth Object Studies) website for more information related to NEOs.
NEOs are a broad category of small-bodies defined as those with a trajectory that can come within 1.3 au of the Sun. Since the Earth orbits at approximately 1 au, such objects can in principle come within 0.3 au of Earth. However, being in the NEO category doesn’t mean they are actually close to Earth at any paticular time, only that their motion can, at times, bring them close to the Sun and possibly Earth.
NEOS are of interest because they have trajectories that make them relatively easy to get to with spacecraft, or observe and charaterize with ground-based radar. Their low surface gravity can simplify spacecraft operations while providing a representative sample of solar system materials and history, since most have evolved into the inner solar system from elsewhere after millions of years of gravitationally interacting with the planets.
A subset of NEOs can potentially impact the Earth, so their trajectories are of particular interest and the focused subject of our related CNEOS website.