Drywall is a type of sheet material for walls and ceilings.
It is made of gypsum, which when mixed with water produces an adhesive paste that hardens in sheets.
Drywall often comes with special paper on one or both sides to make it easier to put up by the drywall professional.
One side has a pattern with lines showing where to cut out holes for electrical outlets, light fixtures, doors, windows, and other items; the other side has an even texture that makes it easy to paint or finish with wallcoverings like wallpaper or paint.
Plaster is a building material used for coating interior walls and ceilings, typically consisting of either plaster of Paris (a mix of lime and water) or gypsum plaster (a mix of gypsum, sand, and water).
The mixture is applied to the surface with a trowel. There are also two-part epoxy compounds for larger areas, which set up in minutes.
So this is the difference between Drywall and Plaster.