I was always told weaknesses are internal and threats are external. Been years since I last did one though
I’ve been told both, depends which management consultant snake oil salesman is sat in front of you.
I suppose you could argue it’s the same thing, an opportunity/threat that’s external requires something to happen (or not happen) to make it a strength/weakness. E.g. your USP is only a strength because there was a gap in the market (an external thing, an opportunity) and you moved the company into it (making it a strength). The threat (external) is that someone else might do the same (and action, making it a weakness).
I prefer the other way of thinking about it as you can then split your opportunities and threats into short, medium and long term items.
short – can do nothing to influence the outcome, can only deal with the consequences. e.g. you’re already on a course to learn something, the opportunity is what you do with it.
medium – can only influence the outcome, but can’t avoid it. e.g. you can see a market crash coming, what’s the plan to cope with it.
long – if you take action now you can influence it happening at all. e.g. you can see the market crash coming, and have time to switch markets entirely.