From Wikipedia:
The Veil Nebula is a cloud of heated and ionized gas and dust in the constellation Cygnus.[4]

It constitutes the visible portions of the Cygnus Loop,[5] a supernova remnant, many portions of which have acquired their own individual names and catalogue identifiers. The source supernova was a star 20 times more massive than the Sun, which exploded around 8,000 years ago.

An invisible object to the naked eye, but easy object of find as it is next to the star Epsilon Cygni.