This is a great question. The balance of trade, to put it simply, is what we import versus what we export. A nation want to export as much as possible, because this is what bring jobs and wealth to a country. Historically speaking, the United States has been the greatest importing nations in the world and one of the three greatest exporting nations in the world.
More recently, there has been a bigger trade deficit. For example, the total March exports was $186.8 billion and imports was $238.6 billion. This is not a promising number, because we are buying more than we are selling. In short, this is not helping the economy. So, what politicians and businesses are trying to do is to export more. We need to create more jobs and hence trading becomes more and more important.