There are three types of "treaties," only one of which requires a two-thirds vote by the Senate--the restricted interpretation of treaties in the US constitution, congressional-executive agreements and sole-executive agreements.
"They are all considered treaties under internal law, but are distinct from the perspective of US law."
Treaties has the force of law and are permanent, but can be repealed by an act of Congress... "By contrast, a congressional-executive agreement can only cover matters which the Constitution explicitly places within the powers of Congress and the President.[1] Likewise, a sole-executive agreement can only cover matters within the President's authority or matters in which Congress has delegated authority to the President."