Can somebody explain to me what a ‘raw vegan’ is?

I read somewhere that a raw vegan does not eat food cooked above 40 degrees. Is this true? And also, why become a raw vegan? I fully understand veganism and vegetarianism because they are saving animals from suffering, I myself am a vegeterian but I don’t understand how the temperature of a food matters? I’m open minded and just want to learn more about raw veganism and what it entails. Thanks