$1m vs. $1MM...what's the difference?

$1m and $1MM can both represent $1,000,000

Typically, in real estate the short hand for $1,000 is $1K, while the shorthand for $1,000,000 is $1m. 

In finance, however, we use $1M to represent $1,000 and $1MM to represent $1,000,0000.

MM in Roman numerals
MM is an abbreviation for millie millia, which in Latin means million. The two words translated separately mean the singular thousand and the plural thousands--a thousand thousands. Together they translate as directly as million.

Example: $1,400,000 Can be expressed as $1.4 million or $1.4mn or $1.4m or $1.4MM or $1,400k or $1,400M.