By Swami Harshananda
Prastara literally means 'that which is strewn.'
In Vedic sacrifices, since the implements used are considered sacred, they should be kept on the vedi in a clean and pure place. Cleanliness is external and physical, purity is more a ceremonial concept.
- The Concise Encyclopedia of Hinduism, Swami Harshananda, Ram Krishna Math, Bangalore