Definition - What does Shiva mean?
Shiva (Śiva) is a Hindu deity with many incarnations. He's part of the Trimurti (alongside Brahma and Vishnu) and represents multiple benevolent paradoxes. Because he was the first yogi from whom all yogic knowledge was granted, Shiva is the god of yogis and yoga practice.
Shiva is called the destroyer, but he's also called the restorer, as his acts of destruction serve to rejuvenate life and energy. Essentially, Shiva is “that which is not.” He's the nothingness that holds everything, doing that which the something can't do.
Yogapedia explains Shiva
Shiva is the source of yogic traditions. When an individual practices yoga and achieves union between mind, body and spirit, they achieve harmony with all things; therefore, they experience nothingness because the ego is destroyed.
Lord Shiva is depicted with a third eye on his forehead. The King of Serpents, Vasuki, is coiled around his neck. A crescent moon rests upon his head and the Ganga river flows from his matted hair. He also possesses a trident and a drum in most images.
Parvati is the consort of Shiva. Some say that Maha Shivaratri, a holiday dedicated to Shiva, marks the day that he and Parvati were wed. It's said that when Shiva is reincarted as an avatar, Parvati is also reincarnated as that avatar's consort. The avatar, Krishna, for example, was accompanied by Radha and the two are often worshiped together. Lord Nataraja, the Lord of Dance, is another incarnation of Shiva.
Shaivism (also spelled Saivism) is one of the main sects of Hinduism and refers to those who consider Shiva to be the supreme being. Shaivism has five sub-sects: Shaiva Siddhanta, Kashmir Shaivism, Vira Shaivism, Gorakhnath Shaivism and Pasupatha Shaivism.