What does "International Law" mean?

The term "international law" generally refers to laws that
are meant to govern what independent or sovereign states do.  These laws typically have
to do with what rules states must follow when interacting with one another. 
International law is typically created by supranational organizations like the United
Nations.

An example of international law would be the
Nuclear Nonproliferation Treaty.  This treaty sets out who may and who may not have
nuclear weapons.  Countries that have signed the treaty are supposed to abide by it and
may face sanctions if they do not.

It is important to note
that states only have to follow these laws if they want to or if other states can make
them.  They may technically be bound by the laws, but there is no way to enforce the
laws other than by having another state or states do it.  We can see this in the case of
Iran and their nuclear weapons.  Other states are either unwilling or unable to enforce
international law in this area and so Iran has gotten away with breaking that
law.

Therefore, international law does not have anywhere
near the force that domestic laws have within countries.