I had to google that. Apparently decimal separator is the one between whole numbers and decimals (ie. 10 dollars 50 cents would be separated with a comma thusly $10,50 and with a period point thusly $10.50)
But then there's group separators or thousand separators, which can also be a comma or period, but also as the internationally recommended way, a space. So 10.000,00 / 10,000.00 / 10 000,00 etc.

I'm not trying to pedantic here. This is actually somewhat of a personal interest of mine because of my job. Spelling numbers in contracts is important because, well, an incorrectly spelled monetary figure could result in a "funny" yet destructive end result.
Where I live we use the international standard thousands separator and decimal comma: 10 000,00
In the US I believe the thousands separator is a comma and decimal separator is a period: 10,000.00
But since the space as a thousands separator is so unambiguous I just use it even on mostly US based forums or websites.

I sometimes see judges using a period as a thousands separator and want to scream at them for it (because WE DO NOT USE A PERIOD THERE!)