Complex sentence: The usual distinction is that powered armor is form-fitting and worn; mecha have cockpits and are driven by pilots, or that powered exoskeletons augment the user's natural abilities, while mechas replace them entirely.
Split into simpler sentences: The usual distinction is that powered armor is form-fitting and worn; mecha have cockpits and are driven by pilots. Some have defined it in that powered exoskeletons augment the user's natural abilities, while mechas replace them entirely.