What is 'the House' in American politics?

The House of Representatives

The American political system has three centres of power. These are  the President and the two chambers in the American Congress the - Senate and the House of Representatives

'The House' is the bigger body because congressmen are elected at a local level while the Senate consists of two senators from each State.

At present the Presidency & the Senate are controlled by the Democrats. The Republicans have a small majority in the House. Legislation has to pass from the House to the Senate and finally to the President. 

Because the two main parties (the Republicans & the Democrats) have major philosophical differences most legislation is contested.