A protoplanetary nebula or preplanetary nebula (Sahai, Sánchez Contreras & Morris 2005) (PPN, plural PPNe) is an astronomical object which is at the short-lived episode during a star's rapid evolution between the late asymptotic giant branch (LAGB)[a] phase and the subsequent planetary nebula (PN) phase. A PPN emits strongly in infrared radiation, and is a kind of reflection nebula. It is the second-from-the-last high-luminosity evolution phase in the life cycle of intermediate-mass stars (1–8 M☉). (Kastner 2005)
https://en.wikipedia.org/wiki/Protoplanetary_nebula
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