Two of the most important and appallingly unaddressed questions of our age.
Here's my best answer, (but I understand that it probably isn't perfect):
Rights are those things that any free adult individual can assert, that the government can guarantee (or direct compensation/retribution if violated) equally for all, and that does not trespass upon the Rights retained by others.
I could assert the Right to pick my nose, and it does not trespass upon the Rights of others, but the government can't guarantee that Right if I have no arms or fingers. Therefore, it is not a Right.
Animal Rights do not exist, because there is no way to monitor and guarantee them for all animals.
Group Rights and preferential treatments like AA are not Rights, because I cannot assert some of them due to the circumstances of my birth (gender, skin color, etc).
a common response to this is that the assertion of any right must necessarily restrict the rights of others (i.e. the right to violate), making this definition contradictory.
can you remind me how libertarians resolve this problem? is a social contract in which the 'right to violate' is waived part of the bargain?