A class 1 nebula
A class 1 nebula was a type of nebula.
In 2374, the USS Voyager encountered a class 1 nebula in the Delta Quadrant containing amounts of protomatter. A shuttlecraft was sent to collect a sample; however, Neelix was fatally injured during the attempt. He was later revived thanks to Borg nanoprobes provided by Seven of Nine, but experienced psychological trouble. Neelix tried to transport himself into the nebula, but was blocked by the bridge crew. (VOY: "Mortal Coil")
According to the Star Trek: Star Charts (p. 88), this nebula was located in an area of space between the B'omar Sovereignty and the Krenim Imperium.