'K' stands for kilo. 'Kilo-' is a Greek-based [I think] prefix that means one thousand, as in kilogram [1000 grams] or kilowatt [1000 watt]. I'm not sure when it was adapted to currency, but surely it was used as a handy shorthand in place of zeroes.
1,000,000 to 1ooo
no
1ooo
1ooo years ago
A millennium is a 1ooo years .
1ooo
1ooo
1OOO DINNER
1/1ooo
Un millier de
1ooo,ooo,oo
10^52