Kurma

Kurma or Kurmaraja is an avatar or incarnation of Lord Vishnu. It is one of the 10 major incarnations (Dashavatar) of Lord Vishnu. Kurma is the second avatar out of the ten dashavatars.

The Churning of the Ocean
In the early times, the devas (god's) and asuras (demons) were mortal. They could die by any means. The only way to gain immortality would be by consuming the divine nectar (Amrit). But the nectar was no share to be found. This led to the constant wars between the devas and the asuras. One day, when the devas were on the edge of losing to the asuras, they went to lord Vishnu for help. Lord Vishnu told them to obtain the nectar of immortality. When the devas asked how, Lord Vishnu told that there is a god, Dhanvantri, in the Ksheera Sagara (ocean of milk) and he has the nectar. The nectar can only be obtained by churning the ocean. When the devas argued that such a huge thing as the ocean cannot be churned, Lord Vishnu suggested that they use the mountain, Mandara as the churning rod and the serpent, Vasuki as the churning rope. But the devas alone couldn't do the task as they were less in number. Lord Vishnu suggested that they use the help of the asuras in this task. So, the devas went to the asuras and requested them for their help telling that they would share the nectar with them. The asuras agreed and the churning began once Mandara and Vasuki were in place. As the churning started, the mountain Mandara couldn't hold still. It was sinking in the ocean. So, Lord Vishnu took the form of a huge tortoise and dived into the ocean to support the mountain. Thus, the devas and the asuras churned the ocean, many valuable things came out of the ocean including the nectar of immortality.

Etymolgy
The word Kurma, in sanskrit, means 'turlte' or 'tortoise'. Kurmaraja means 'king of tortoises'.