Class 17 nebula

From Memory Alpha, the free Star Trek reference

A class 17 nebula is a type of nebula containing hydrogen and helium.

In 2373, the USS Voyager encountered a type 17 nebula in the Delta Quadrant containing 7,000 parts per million of sirillium. It was somewhat similar in composition to the class 11 Azure Nebula near Klingon space in the Beta Quadrant. (VOY: "Flashback")