Chondrites are the most primitive meteorites known. That is, they are the most ancient ones in terms of when their constituents came together to form a rock, and the most unprocessed ones in terms of how little their materials have been altered since this rock formed. Achondrites, on the other hand, lack chondrules and represent more processed materials. Chondrites, achondrites, stony-irons and irons are subdivided into groups and subgroups. These will be presented in more detail below.
Falls are meteorites whose arrival on Earth was witnessed and recorded.
Their time of fall is thus relatively precisely known. These meteorites were usually recovered shortly after their arrival, although often enough in the case of showers, additional fragments from a given fall may be recovered a long time after the fall occurred. When all falls exclusively are considered, a reasonably good estimate of the general population of meteorites reaching the Earth may be made. In other words, most meteorites falling on Earth are by far chondrites. Finds are meteorites that were not seen to fall but were subsequently discovered on the ground, often long after they landed.