That is the number of popular votes that Hillary Clinton had over Donald Trump. It was a number that was 2.1% more of the popular vote than Donald Trump won.
That is a number which is larger than the population of 16 States and District of Columbia (Nevada, New Mexico, Nebraska, West Virginia, Idaho, Hawaii, Maine, New Hampshire, Rhode Island, Montana Delaware, South Dakota, Alaska, North Dakota, District of Columbia, Vermont, and Wyoming). It is slightly less than the populations of 4 States: Mississippi, Arkansas, Kansas, and Utah). It is slightly more than the combined populations of Alaska, North Dakota, District of Columbia, Vermont, and Wyoming (2578472).
It's also a number which is larger than most of the 100 largest US Cities (Only NYC and LA have a larger population).
It's not an insignificant number, yet somehow Clinton lost with one of the highest margins of the popular vote because of the Electoral College and how it distorts the vote.