What does it mean even? And odd? I'm actually an international student and I'm not very confident with specific mathematical terms. I was doing some exercises when I came up to the words even and odd. What do they mean exactly?
Here's the context:

Which of the following relations are even?
I. something
  II. something 
  III. something
Results:
  (A) only I (B) only I and II (C) ... (D) ...  (E) ...
Which of the following relations are odd?
I. something
  II. something 
  III. something
Results:
  (A) only I (B) only I and II (C) ... (D) ...  (E) ...

Thank you very much!

A (binary) relation $R \subseteq X \times Y$ is said to be even, if whenever $(x,y) \in R$ so is $(-x,y) \in R$. A binary relation is called odd, if whenever $(x,y) \in R$ so is $(-x,-y) \in R$.
Wasn't sure either at first, but the term is generalized from the usage in the study of functions (for a source see here).
