The assignment is to write an essay explaining a concept. My teacher is pretty unclear what she means. Any ideas?

Answer 1

This type of essay is also called an expository essay:
http://owl.english.purdue.edu/owl/resource/685/02/

A concept is an idea. Yes, it's that vague! So it sounds as if you can choose just about any concept/idea you want and then write a paper to explain what it's all about. Answer these questions in your paper: why, who, how. Answer other questions, if needed.

Here are some possible topics:
http://712educators.about.com/od/essaysparagraphspapers/a/academic_expos.htm