A cis-Neptunian object is, literally, any astronomical body found within the orbit of Neptune. However, the term is typically used for those distant minor planets other than trans-Neptunian objects: that is, all sub-planetary bodies orbiting the Sun at or within the distance of Neptune, but outside the orbit of Jupiter. This includes the icy minor planets known as centaurs and the Neptune trojans.
Centaurs orbit the Sun between Jupiter and Neptune, often crossing the orbits of the large gas giants. There is an emerging sense that the centaurs may simply be objects similar to scattered-disc objects that were knocked inwards from the Kuiper belt rather than outwards, making them cis-Neptunian rather than trans-Neptunian scattered-disc objects.