Rabarber is the Swedish word for rhubarb. Rhubarb is the fleshy, edible stalks (petioles) of species and hybrids (culinary rhubarb) of Rheum in the family Polygonaceae, which are cooked and used for food. The plant is a herbaceous perennial that grows from short, thick rhizomes. Historically, different plants have been called "rhubarb" in English.
In essence, rabarber, or rhubarb, refers to the edible stalks of the rhubarb plant that are commonly used in cooking.
