What is terabithia?

Interview of the author:

"I thought I made it up. Then I was rereading C. S. Lewis's The Voyage of the Dawn Treader and realized there is an island in there called Terebinthia. I was appalled and at first thought I must change the name of my imaginary country; but that was so much work that I decided Leslie Burke would have done the same thing. She read those books and she made up a name of a country something like something she had read. And of course, Lewis got Terebinthia from the terebinth tree in The Bible. So I decided if he could borrow it from the Bible, I could borrow it from him - even if I hadn't meant to."