A circumstellar envelope (CSE) is a part of a star that has a roughly spherical shape and is not gravitationally bound to the star core. Usually circumstellar envelopes are formed from the dense stellar wind, or they are present before the formation of the star. Circumstellar envelopes of the old stars (Mira variables and OH/IR stars) eventually evolve into protoplanetary nebulae, and circumstellar envelopes of the young stellar objects  evolve into circumstellar discs.
Types of circumstellar envelopes
- Leao; Patrick De Laverny; Mekarnia; De Medeiros; Benoit Vandame (2007). "The circumstellar envelope of IRC+10216 from milli-arcsecond to arcmin scales". arXiv: [astro-ph].
- Leslie Looney; Lee Mundy; Jack Welch (2003). "Envelope Emission in Young Stellar Systems, A Sub-Arcsecond Survey of Circumstellar Structure". arXiv: [astro-ph].