The "Bush tax cuts," enacted in 2001 and 2003, are set to expire at the end of the year. Democrats want to let them expire for families with an annual income of more than $250,000 and single earners with an income of more than $200,000. Republicans want to extend the cuts for everyone.
The graphic above, from The Washington Post, shows the cuts people in different brackets would get under the two plans. As you can see, the big difference is that millionaires do much, much better under the Republican plan. The standard defense for that plan—which might otherwise just look like a huge gift to the most fortunate among us at the expense of the public good—is that lots of these high earners are, in fact, small businesses owners. That's debatable, to say the least.
Letting rates jump back up to Clinton-era levels for high earners, by the way, would reduce the deficit by $36.6 billion.