A fairly simple one (but one I can't seem to find a definition for anywhere), so sorry if it shouldn't be in the advanced section.

What is the difference between right and left eigenvectors?

For example I have

(2/3 1/3)

(1/6 5/6)

Found eigenvalues 1/2 and 1, and eigenvectors (-2,1) (1,1) respectively. But which is the right eigenvector?!

Thanks