Aside from what others have mentioned (tons of them do use the term open source), "open weight" is deliberately meant to parallel "open source" but in practice

Aside from what others have mentioned (tons of them do use the term open source), "open weight" is deliberately meant to parallel "open source" but in practice it doesn't. Most "open weight" models have usage restrictions that would make a code license most definitely not open. The right term for most of these models would be "weights available".