Are you finding mkl_def.dll just press download button to get your mkl_def.dll file.
If some software in your windows OS wants mkl_def.dll your operating system will ask for DLL file. When that DLL file is not available you will get this error.
If you have moved your file or changed the name of dll file you will get this error.
You will mostly see there errors when you dll file is missing:
If you need mkl_def.dll Download it right now and install it into your system to fix the error as soon as possible. just Install mkl_def.dll and fix your error.