Oppression Vs. Privilege
Oppression is a system whereby:
1) A group “A” is systematically mistreated in comparison to non-As in a given social context.
2) The distinctive traits of group “A” are viewed as exceptions to the “unmarked” or “default” traits of a “normal” member of society.
3) Members of group “A” are effectively prevented from holding a significant number of high leadership positions in society’s controlling institutions.
Privilege is a system whereby:
1) A group “B” is systematically, unfairly advantaged in comparison to non-Bs in a given social context.
2) The distinctive traits of group “B” are viewed as the “unmarked” or “default” traits of a “normal” member of society.
3) Members of group “B” hold a near-monopoly on the high leadership positions of society’s controlling institutions.
My first thought, left in the comments at Alas, is that I would remove point 3 from both definitions — lack of leadership positions is a likely consequence (and a common reinforcing mechanism) of oppression as defined in points 1 and 2, but I don’t see why it needs to be elevated to definitional status. Also, it’s potentially distracting, since it implies that "number of As in leadership positions" is a simple measuring stick for level of oppression (and there are cases where I’d say oppression is still present despite things being fine on the number-in-leadership front — Christians being privileged over Jews comes to mind).
Second, I would change "non-A" to "B" in the oppression definition, because oppression is always relative to a specific oppressor group. For example, black people are oppressed because they're systematically mistreated relative to white people, but not necessarily relative to any other non-black group such as Native Americans.
Finally, I think that while points 1 and 2 are both part of both definitions, I would reverse their order in the case of privilege. As I see it, the core of the concept of oppression is the harm it does to the oppressed -- being oppressed means bad stuff happens to you in a particular way. In the case of privilege, on the other hand, I think the mechanism is what's central. Privilege is about being seen (by yourself and others) as unmarked and normative, and feeling entitled to have the world operate on that assumption. Advantages flow to the privileged person, and harms to the oppressed, as a consequence of that mechanism. When one person tells another "check your privilege," they aren't saying "think about how good you have it!" so much as they're saying "remember that not everybody is, or should be, like you!" It's a subtle distinction, because the two parts do go together, but I think the words are not quite opposites because they stress different elements of systemic inequality.