There are at least two good ways to define Jacksonian democracy. One is by talking about its ideals and beliefs, while the other is by talking about the policy positions that sprang from those beliefs.
Ideologically, Jacksonian democracy can be defined as a very populist form of mass democracy. We say that it was a mass democracy because it believed that the common people should be involved in the political system. Before this, politics had been dominated by members of the elite like Thomas Jefferson and George Washington. Jacksonian democracy believed that the common people should have more control over government. Jacksonian democracy was populist because it believed that the needs of the common people should be placed ahead of the needs of the elites.
Jacksonian democracy can also be characterized by looking at the policies that it preferred. Basically, Jacksonian democracy believed that excessive government was typically used to help the elites to dominate the common people. For this reason, Jacksonians wanted to have government do fewer things. They wanted a more laissez faire government that would not take actions (such as the creation of the Second Bank of the United States) that would help the elites at the expense of the common people.
Thus, Jacksonian democracy was a political ideology whose beliefs and policies were based on the ideas of populism. It believed that the common person (or at least the common white male) should have more control over government and that government should do things that would benefit him rather than the elites.