I have searched around and it seems that there is no consistent consensus on what a code sample should contain.

-Some think it should be a full program that has been specially crafted to be short and show off some of your understanding.

-Some think that it should be an excerpt from a larger project that highlights something you think is relevant and cool.

-Some think that the size doesn't really matter as long as it contains the full project, is buildable, and is relevant.

Does anyone know if there is a generally accepted definition for what a code sample is when it comes to game studios?

Does anyone know if there is a generally accepted definition for what a code sample is when it comes to game studios?

There is not!
Tailor a code sample to the company and position. If they are hiring you to be a shader wizard, submit some clever shaders. If they are hiring you as a lead/architect then a completed game might be a better choice, etc.