Question

Can anyone take a stab at defining a thesis statement?

Answer 1

an explanation of the topic or purpose of a research paper

Answer 2

A topic sentence giving a brief explanation of what you are going to discuss in your paper.

Answer 3

Like stolas and angelpeach said, it is a topic sentence that explains what you are going to discuss. In an argumentative paper it should give your position on the topic. Each following paragraph should be a proof or explanation of your thesis in some way.