The word "Saiya" has no real meaning and it's just a word Akira Toriyama made up. The Japanese way of saying it is "Saiya-jin", but in the English version, it is pronounced "Saiyan". The Saiyans are a race of fighters/warriors. Because of the way and purpose if fighting, they can also be called barbarians. Since their way of life is kill, fight, kill, fight, kill, fight, and win, they live longer than humans and sustain their youth. Their hair never grows forever, which means when their hair is at a fixed length; it doesn't grow anymore and another weird thing about their hair is that they're born with hair that is at their fixed length. The reason for the tail is because when full moon-light hits them, they turn into these monstrous ape-things, thus multiplying their power level by 10. The Saiyans fight, not only for the fun of it, but because it's their job. They are apart of a planet trade where they go to different planets that might bring up a good price and they "rid" all the life on it. The big boss behind all of it is Freeza, known to be the strongest being in the whole universe. Since Saiyans grow stronger every time they fight, Freeza was afraid that they might over throw him. He wasn't afraid of one getting stronger because none of the Saiyans were anywhere close to his power level, but he was afraid of them in numbers, so he destroyed the planet and everything on it. Only 4 Saiyans survived....