A protoplanetary disk (or proplyd) is a rotating circumstellar disk

Circumstellar disk

A circumstellar disk is a torus, pancake or ring-shaped accumulation of matter composed of gas, dust, planetesimals, asteroids or collision fragments in orbit around a star. Around the youngest stars, they are the reservoirs of material out of which planets may form...

 of dense gas surrounding a young newly formed star, a T Tauri star

T Tauri star

T Tauri stars are a class of variable stars named after their prototype – T Tauri. They are found near molecular clouds and identified by their optical variability and strong chromospheric lines.-Characteristics:...

, or Herbig Ae/Be star. The protoplanetary disk may be considered an accretion disc

Accretion disc

An accretion disc is a structure formed by diffuse material in orbital motion around a central body. The central body is typically a star. Gravity causes material in the disc to spiral inward towards the central body. Gravitational forces compress the material causing the emission of...

 because gaseous material may be falling from the inner edge of the disk onto the surface of the star, but this process should not be confused with the accretion process thought to build up the planets themselves.
Protoplanetary disks around T Tauri stars differ from the disks surrounding the primary components of close binary systems in their size and temperature.