Shiv Chalisa

Shiv Chalisa (Hindi: शिव चालीसा, literally Forty "chaupais" 
on Shiva) is a devotional stotra dedicated to Hindu deity, Lord Shiva. Adapted from the "Shiva Purana", it consists of 40 (Chalis) chaupais (verses) and recited daily or on special festivals like "Maha Shivaratri" by Shivaites, and worshippers of Shiva.
Shiva.
Shiva is a major Hindu deity and the Destroyer or transformer of the Trimurti. Shiva is usually worshipped in the abstract form of Shiva linga. In images, he is generally in deep meditation or dancing the Tandava. Lord Mahesh or Shiva, one of the Hindu Trimurti, is the Destroyer. He represents the form of sada shiva the creator of universe. His attributes represent victory over the demonic activity, and calmness of human nature.
According to linga Purana and shiv mahapuran he is the creator of the universe and father of brahma,vishnu and rudra .He is nirguna i.e. free from nature and most powerful.
Overview.
Lord Shiv is the Hindu Trinity of the primary aspects of the divine which have dominion over death and destruction. He appears in a meditating but ever-happy posture having matted hair which holds the flowing Ganges river and a crescent moon, a serpent coiled around his neck, a trident (trishul) in his one hand and ashes all over his body. He is known as the "giver" god. His vehicle is a bull (symbol of happiness and strength) named Nandi.
Shiva-Linga, a sign of the Lord, is adored instead of him. Shiva is also considered the greatest of the yogis, the lord of meditation, and the lord of all that is in Hindu practices. Legend has it that the holy river Ganges (or Ganga) is in fact a representation of Lord Shiva's long hair.
Some texts refer to the five letters as the forms of Shiva - Na-gendra (one who wears a garland of snakes), Ma-ndakini Salila (one who is bathed by the water of the Ganges), Shi (the supreme Lord), Va-shishta (one who is praised by the sages like Vashishta), and Ya-ksha (one who takes the form of Yaksha). The Om Namah Shivaya mantra or chant consists of six syllables - om, na, mah, shi, vaa, ya. The Shiv Chalisa are 40 chaupais (verses) is written in praise of Lord Shiva.