Odin is a utility software developed and used by Samsung internally. It can be used to flash a custom recovery firmware image (as opposed to the stock recovery firmware image) to a Samsung Android device. Odin is also used for unbricking certain Android devices.
There is no account of Samsung ever having officially openly released Odin, though it is mentioned in the developer documents for Samsung KnoxSDK and some documents even instruct users to use Odin . Some other docs on Knox SDK reference "engineering firmware", which presumably can be a part of the Knox SDK alongside with Odin. Publicly available binaries are probably believed to be the result of leaks.