PAL DVDs have 576 pixels of vertical resolution, vs the NTSC standard which has only 480. Every DVD drive can handle both formats, but some DVD players sold in the US won’t accept PAL format discs, even if they’re region free, just as some sold in Europe won’t accept any NTSC discs, even if they’re region free.
Off brands are usually the ones which don’t really care what format disc you use in them, and there’s several brands that don’t even bother reading the region code.
But yeah, there’s a difference in format. I’d better know this, my wife lists 450 DVDs on eBay each day and she’d probably kill me if I got that wrong. :)
“But yeah, there’s a difference in format.”
Indeed there is. On the other hand, having lived overseas and used a variety of DVD players and TV sets I never came across a DVD that wouldn’t play. I’m not sure the issue of PAL or NTSC has the same impact as it did with old VHS tapes.