Unspecified is a special pin type that is used to make a generic symbol in the global library with the expectation that the user of the symbol makes a derived project specific symbol where they specify the correct pin type. This is useful for configurable pins if one wants to force users of the symbol to specify the pin with the best possible pin type for ERC.
Details about pin types: Electrical type of schematic symbol pins (KiCad 4 and KiCad 5)