Forward compatibility

Forward compatibility is 前向兼容 in Chinese, aka Upward compatibility, which is a design characteristic that allows a system to accept input intended for a later version of itself.

Backward compatibility

Backward compatibility is 后向兼容 in Chinese, aka Downward compatibility, which is a design characteristic that allows a system to accept input intended for a older version of itself.

The main difference between these two is the relation between system and input. For an example, the Python interpreter is a system and a python script file is the input. We will say Python 3.X interpreter is NOT Backward compatible for it cannot interpret some Python script files(input) which is written under the Python 2.X standard.