Today is the day that members of the United States Electoral College meet to cast their votes for president. That means that, barring an upset of unprecedented and earth-shaking proportions, today is the day that Barack Obama officially becomes president-elect, and Joe Biden officially becomes vice president-elect.
I wouldn’t hold your breath waiting for a electoral upset, but in case you are interested, may I suggest Wikipedia’s excellent articles on both the Electoral Collage itself (did you know that the Constitution forbids electors from holding federal office?), and faithless electors (electors who don’t vote for the candidate to whom they are pledged). Faithless electors are rare, but not unprecedented: one of Washington, DC’s electors abstained from casting her ballot in 2000 in protest against DC’s “colonial” status, and a rogue Nixon-pledged elector in 1972 cast the first ever electoral vote for a woman (Theodora Nathan, vice-presidential candidate on the Libertarian Party ticket, in case you were wondering).