Msg 243 Level 16 - Is not a defined system type

On Transact SQL language the Msg 243 Level 16 - Is not a defined system type means that the date type is misspelled or does not exist.

Msg 243 Level 16 Example:

Invalid select:

SELECT CONVERT (time123, GETDATE()) as System_time,
CONVERT (datetime2, GETDATE()) as System_datetime2;

Message
Msg 243, Level 16, State 1, Line 1
Type time123 is not a defined system type.

Correct select:

SELECT CONVERT (time, GETDATE()) as System_time,
CONVERT (datetime2, GETDATE()) as System_datetime2;

System_timeSystem_datetime2
15:55:19.78000002014-09-06 15:55:19.7800000

Other error messages: