The Tarids are race of humanoids who live on Thuria (Phobos), the nearer moon of Mars. They look, for the most part, like the Red Martians, except that their skin is white and their hair and eyebrows are blue. They also seem to lack the vitality of the Martian races; When John Carter encountered them, he was struck by the fact that many of them showed signs of age, which is not commonly seen among Martians. They worship the Sun, which they call the Blood God.
In the distant past, the Tarids were a powerful and vast empire stretching across the face of Thuria, which they call Ladan. But they were nearly wiped out in a war with another nation, and the survivors of the once-great empire are now all holed up in a large castle, only about a thousand remain. Believing that all of the other races seek to destroy them, they have developed the ability to hypnotize others so that they appear invisible.
The term Tarid does not actually seem to refer to the race as a whole, but rather a specific group. There are members of the same race on other parts of the moon equally capable of learning to use the hypnotic abilities that render the race invisible.