Beyond Selidor

lokifan has it right in the previous comment. The name originates in their economic liberalism — an emphasis on low taxes, free trade, and minimal government intervention in economic issues. (This is generally the ideology behind the names of most 'liberal' parties in Europe as well.) Obviously economic liberalism doesn't have to go together with social conservatism, but in practice this is how it's worked in Australia when it comes to our largest centre-right party.

This is in contrast to our other major party, the centre-left Labor Party, which started out with a social democratic approach when it came to economics (higher taxes, more state support for social services such as health and education), and ultimately found that this went together more naturally with a more progressive approach to social issues. (Although many progressive Australians would quibble with my characterisation of Labor and say that they've drifted too far to the centre.)