山丘 (pl. tholi)是在行星地质学用来描述一个小小的圆顶的山或小山。这个词是从希腊文θόλος 转过来的，原本的意思是有着圆锥形或拱形屋顶的建筑物，罗马人翻译这个字成为拉丁文的tholus，意思是圆顶 (cupola) 或 窟窿 (dome)。 在1970年代早期，国际天文学联合会 (IAU) 将tholus作为官方描述火星和其他行星与卫星地形特征的术语。使用中性的拉丁文或罗马字描述的理由是在其地质或地貌被测量或确认之前，就可以为它命名 。例如，许多山丘似乎是源自火山，而这个名词并未意味着特定的地质成因。目前，IAU确认了54个术语 (参见行星命名)。山丘使用在金星、火星、和木星的卫星艾欧。.

In planetary nomenclature, a tholus (pl. tholi) is a small domical mountain or hill. The word is from the Greek θόλος, tholos (pl. tholoi), which means a circular building with a conical or vaulted roof. The Romans transliterated the word into the Latin tholus, which means cupola or dome. In 1973, the International Astronomical Union (IAU) adopted tholus as one of a number of official descriptor terms for topographic features on Mars and other planets and satellites. One justification for using neutral Latin or Greek descriptors was that it allowed features to be named and described before their geology or geomorphology could be determined. For example, many tholi appear to be volcanic in origin, but the term does not imply a specific geologic origin. Currently (March 2015), the IAU recognizes 56 descriptor terms. (See Planetary nomenclature.) Tholi are present on Venus, Mars, asteroid 4 Vesta and on Jupiter's moon Io.