With this technique, a countless number of summoned snakes crawl out of Orochimaru's mouth and hunt down the enemy. With such overwhelming numbers, a true "wall of snakes" is formed, making defence and evasion meaningless. The enemy can do nothing but become buried by the snakes. The snakes can bite the enemy with their poison fangs and open their mouths to extend Kusanagi-like blades, making them even more deadly. Furthermore, when the inexhaustibly crawling snakes gather together, they become a defensive wall, and can block any kind of attack.
Mandara is the Japanese pronunciation of the word mandala, a concentric diagram with great spiritual and ritual significance in both Buddhism and Hinduism. It's written as 曼陀羅 in kanji. The first kanji is pronounced the same as the kanji for ten thousand (万) and actually overlaps somewhat in meaning. The second kanji bears a strong resemblance to the kanji for snake (蛇). The last kanji is the same in both words and means silk, or gauze. However, it is only used for its sound.
This technique is part of other technique that appears in Naruto Shippūden: Ultimate Ninja 5, called "Uwabami", but the snakes that Orochimaru spits don't spits swords and attack the enemy like a tsunami.