Definitions of Liberalism
A definition based on the history of the Liberal Party
The Origins of the Liberal Party
The origins of the party were all about the control and dispersal of centralised power. Support for religious dissenters was soon added, and hence pluralism in general and individual freedom. They were based to some extent on the ideas of Locke  on constitutional government and the ultimate accountability of government to the people and on those of Milton  on religious and political liberty.
Conrad Russell  makes it quite clear that the Liberals did not have any particular economic approach as part of their values, and therefore followed current fashion. As he points out, Mill  approved free trade on pragmatic grounds. However, Mill  earlier justified laissez-faire, and gave its limits, on the grounds of each individual knowing what is best for them; interestingly, he asserted that the joint stock company was no better than government bureaucracy.
The Home Rule Split and the Rise of the Modern Left-Right Question
The split of the Liberals over Home Rule, along with the widening of the franchise, caused a realignment. Aristocratic support no longer being enough, the Conservative Party became a coalition of much of the aristocracy and middle classes, based on the importance of the rights of property. The Liberal Party emphasised the rights of the individual: powerless people should always be protected against the powerful, whoever they are. So Liberal values got new emphasis within the new context. Green  introduced the idea of community or society as a way of individuals expressing their will, opening the way to a more active but Liberal government.
The rise of the Labour movement then caused a problem for Liberals. Using laws to limit the power of owners over employees was clearly Liberal, and using the state to provide for the worst off was a natural development, since rights surely extended to basic standards. Hobhouse  justified this as naturally Liberal. However, when many wanted to use the power of the state to counterbalance the power of capital, which side should Liberals take? In the Liberal Yellow Book , the Liberal Party defined its economic approach, including the control of company power internally, rather than by the state. It was widely read, but the party soon ceased to be influential.
New Ideas and Liberal Revival
The Liberal Party invented Community Politics , which applied liberal decentralisation to the provision of local government services. Its key idea was of people influencing their own lives by joint campaigning and political action. This is a way to achieve one of the main liberal values, which was for a while emphasised over the others: that people should have the maximum control over their own lives. This gave the party a clear image rooted in our historic values, and a focus for campaigning.
The other new idea was environmentalism. I have suggested a link with liberalism at the personal level, rather than a logical link. However, the political influence of the idea first came outside the party. Rather than helping us, it almost buried us at the European elections, and damaged our confidence, certainly on European questions. It was mainly the work of committed environmentalists within the party that has changed the position.
With the formation of a new party, there were attempts to define what we stood for [10, 11].
With both the other parties becoming authoritarian, the Lib Dems were then able to assert their liberalism again, although there was the temptation of the (temporarily?) vacant left. Fortunately, public expenditure is the one area that the priorities of liberals and the left were found to overlap, so we started with a liberal but easily placed idea.