Shimenawa is a twisted rope that marks an object or place that is sacred or that has been purified.
A shimenawa may be found on the tori entrance to a shrine, around a sacred object such as a tree or rock, or above a kamidana (home shrine).
There are often shide (gohei) hanging between the tassels on the shimenawa. The shide represent the spiral of energy between heaven and earth. The symbolism is also explained as thunder (the tassels on the shimenawa) and lightning (shide).
The origin of shimenawa goes back to ancient times when Amaterasu no Ō Kami, kami of the sun, hid herself in a cave after an argument with her brother Susanō. After being enticed to peer out, amystical rope was placed behind her so she could not go back into the cave. The universe thus returned to its previous state of illumination. The rope became known as shimenawa.