what's the def of "set-like" in the binary relations?

[ssibseya]

In the wiki, "http://en.wikipedia.org/wiki/Binary_relation"

set-like: for every x in X, the class of all y such that yRx is a set. (This makes sense only if we allow relations on proper classes.) The usual ordering < on the class of ordinal numbers is set-like, while its inverse > is not.

I can't understand "This makes sense only if we allow relations on proper classes."...
And what the "ordinar numbers" above paragraph?

[mavropnevma]

Don't worry - just subtleties of fundamenta of set theory! And it is "ordinal", not "ordinar" (it refers to Cantor's ordinals, for example is the first transfinite one).
But again, don't worry. If interested, read an introduction to set theory book.