A claim refers to a statement that says that something is true. This doesn't mean the information given is actually true. Remeber that we use claims everyday when stating our opinion or sharing facts. In literature they present the author's opinion or main ideas which need to be supported with empirical evidence and trustworthy data, in this way the main idea can be sustained.
For example, I can say: Dophins are more intelligent than chimpanzees.
This is a claim, you don't know for certain if it is true or not, it is my job to give arguments to support that information. In this case, information developed by scientists that have compared these animals.
