backward compatibility; downward compatibility
upward compatibility; forward compatibility; compatibility with input or components intended for higher tier or later systems, versions, etc.; downward compatibility; backward compatibility; compatibility with input or components intended for lower tier or older systems, versions, etc.
downward compatibility; backward compatibility; compatibility with input or components intended for lower tier or older systems, versions, etc.; upward compatibility; forward compatibility; compatibility with input or components intended for higher tier or later systems, versions, etc.