Progressive taxation, also known as variable taxation is a tax system where resident's in a country / area are made to pay a certain amount of tax which is based on their own financial income and living situations rather than taxing everyone the same amount. For example, a person with low income living in a small one bedroom flat would pay less in tax than a billionaire living in a mansion, spending his day eating giant watermelons.
This type of taxation is popular with the Left wing. It is this policy which sparked fear in rich American Republicans that Barack Obama is actually a socialist and may turn into the new Stalin. Apparently wanting to help people afford food rather than tax people into starvation now makes you a dictator. The opposites of progressive taxation are flat taxation or the even more extreme Poll tax.
Progressive taxation recognizes that taxes must be collected from those with the ability to pay.
Progressive taxation try's to assign the costs of government, in proportion to gain from society.
In effect, progressive taxation attempts to tax marginal wealth. If 1% of the people realize 30% of the capital increase, they would be expected to pay for 30% of the infrastructure which enabled the gain.
Sales tax etc
These are taxes on purchased goods, in the European Union the equivalent is Value added tax. Sales taxes can be progressive or regressive depending on which goods are taxed. Taxing basic goods like bread is regressive because poor people spend a high proportion of their incomes on basics. Taxing expensive luxury goods that rich people tend to buy is progressive.
That's not Liberalism. Liberals recognize that social stability is necessary, and that extreme need creates desperation and instability. People may not have the right to expect Capitalists to provide them the good life, but Capitalists don't have the right to exploit people for the sole benefit of Capitalists either.