LiberalismIn its original, nineteenth century sense, liberalism is the political term for the theory which shows that in any evolving system, there is a natural selection of subsystems by survival of the fittest with respect to the feedback sent by the system. The practical corollary is that to achieve the best state possible with respect to the system's natural constraints, you must allow the fairest competition, and the broadest liberty, so that people may automatically adapt to all of these constraints.
The accumulation of data throughout history, that follows this selection, as well as the data accumulated as a result, is called tradition.
Liberalism is commonly applied to economy, where it tells that to achieve prosperity, you must firstly allow the fairest (not the wildest) competition between companies to have the quickest adaptation. Fair vs wild means that information should be freely available, and discussion freely allowed, so that people may compare and choose; choice should be free, and not just based on everyone's (or worst, a few ones') prejudices.
Competition means that free enterprise (not free crookery) mustn't be discouraged in any way, so that small businesses may smoothly fill any dynamically appearing opportunity to achieve better adaptation, however small the opportunity.
Particularly, trusts and monopolies should be fought whenever they eventually appear, and strictly, democratically, controlled when they are inevitable. Liberalism opposes any kind of such centralized, public or private, management. State is made to create and enforce Laws, and nothing else.
Liberalism does not apply only to economy, as show the works of John Stuart Mill in the moral sciences, Charles Darwin in the natural sciences. Some even speak about economical or biological Utilitarianism, or moral or social Darwinism! The current continuators of this philosophical trend may well be the cyberneticians and memeticians.
But beware, many people that call themselves (or are called) liberal do not refer to this original liberalism, but to some degenerate tradition, that misunderstands the deep ideas behind it, and only retain the apparent conclusions of a time, that may well be partial or obsolete. Often, they don't even care about the ideas and just join because they hope to benefit from some prestige related to a "liberal" tradition.
In particular, in the USA, the name "liberalism" has been stolen by a socialist party, whereas socialism is the exact contrary of original liberalism: socialism pretends to achieve adaptation through centralized management. For this reason, authentic liberals sometimes call themselves "libertarian", whereas in other countries, this word only coins anarchists, proponents of absence of state. Though the word "liberal" may be historically attached to such people and their parties, it is not in that meaning that the TUNES project refers to this word. The Democratic party in the USA, which you are presumably referring to, is a capitalist party, and most certainly not socialist. It is similar in some ways to Europe's Social Democrat parties.