According to Hindu religion, It is believed that on Maha Shivaratri, Lord Shiva married Goddess Parvati and according to the Hindu calendar, Shivaratri is marked every luni-solar month.

Why Parvati’s month fainted after seeing Lord Shiva

The wedding of Lord Shiva and Parvati was organized in a grand fashion. Parvati was the daughter of the Daksh the king North Himalayas .
On behalf of Parvati, the Daksha invited all his relatives but there was no relative from Shiva. Because Lord Shiva do not belong to any famly. Lord Shiva is Pashupati, it means the God of all beings.
Parvati’s mother Prasuti was eagerly waiting for her son-in-law standing at the door on the wedding day. As soon as she saw the form of Shiva, she screamed and came inside the house and started cursing Parvati.
This marriage will not take place, the ashes on the body, the jatukdhari, the snake wrapped, the neck garlands and the garlands of glids, whose ghosts, vampires will not marry their daughter, she said.
Somehow after agreeing to the King Daksha she agreed.