Given a curve C, and a reductive group G, there is a moduli stack Loc\_G(C), the stack of G-local systems. I keep reading that there's a substack of "opers" but am having trouble locating a definition. So what's an oper, and how should I think about them?



What is an Oper?
Look at <http://arxiv.org/abs/math/0501398> (*Opers*, Beilinson and Drinfeld, 1993/2005)


