The Universe is an Uncaring Void
I've seen sources say "3x5" (three sets of five) but denote their workouts as 100x5x3 (100 pounds, 5 reps, 3 sets). I've also seen sources say "3x5" and write 3x5 and mean three sets of five in both cases. There is no clear answer to your question. YxZ is fundamentally ambiguous.
Show Your Units
In physics, I was taught to never leave the units ambiguous in our calculations. "5" means nothing; "5 Newtons" means something. I think that advice applies here too. We have competing standards each trying to be the One True Answer. Our only reasonable course of action is to somehow indicate that 3x5 in this case means three sets of five rather than five sets of three.
I independently developed two methods of showing my units: marking my sets as I complete them, and putting commas between "x reps" to show different sets.
The Ticking-Off-Sets Method
I do this haphazardly in my own training notes, either simply remembering, or ticking off sets as I complete them:
Front squat: 45x5, 95x5, 145x5, 195x5x3 '''
This says I warmed up my front squat with a set of five each at 45, 95, and 145 pounds before my work sets. The three tick marks at the end show that I completed three work sets, telling me-six-months-from-now that I meant three sets of five. I certainly don't think this method is optimal.
The Comma Method
Another method I use refuses to write down the number of sets at all, but instead demarcates sets with commas, like so:
Front squat: (45,95,145)x5, 195 x5,x5,x5
This says the same thing as above--three warm-up sets, then three work sets. I think this is perhaps my most unambiguous and concise notation, making it the best.
It has a drawback that is also a benefit: it accounts for failures. This is good, because it minimizes scratching out "3x5" when I fail at the last set. It's bad, because it reduces the consequences and certainty of completing the sets as planned.