Liberal: A person who doesn't wish to uphold the established order of things just for the sake of it; the opposite of conservative.
Can also simply mean a person who is willing to accept change where a conservative would be more hesitant to change up things.
A liberal would be willing to change how things work, if they perceived the current order of business unsatisfactory.
Conservatism can be driven by devotion to ideology behind how things are perceived to be, OR it can simply be an aversion to change in general without ideological basis.
Former would be exemplified by people who, say, think that homosexuals shouldn't be allowed to marry because they perceive it against their religion or religion-derived ethics, or resist NHS because they think it's communist. In this case, their resistance to change is derived from changes being perceived as against their personal beliefs, ideology or code of conduct in general.
Latter type of conservatism would be exemplified by the Ents, ho hummm, or in general people set in their ways and hesistant to experiment with new things with issues that they perceive as working just fine as they are.
Note that liberals can be just as driven by their personal idologies and belief systems as conservatives; the only difference in this case is who happens to represent the current order of things.
Liberal-conservative axis pivots around change and people's readiness or willingess to approve of new things.
On the other hand:
Libertarians (see libertarianism) are the people who emphasize individual liberties as the most important thing to uphold in politics. Both liberals and conservatives can exhibit libertarian views.
By contrast, authoritarian politics would limit freedom and liberties in favour of a more... authoritarian regime, where the liberties and rights of individuals can be disregarded if the figures of authority deem it necessary (see USA PATRIOT act).
I have often seen political orientation represented as a plane with two axes: Horizontal axis representing the economical views (capitalism/socialism) and vertical axis representing authoritarian/liberal politics. In my opinion, however, the authoritarian/liberal comparison is incorrect, as the two are only related by proxy, since it just so happens that conservative politicians in the US tend to have more authoritarian view than liberal politicians (who often have libertarian views, but not always).
A better representation of the political gamut would be a three-dimensional space with economical axis, freedom axis and change axis.
On economical axis you would have capitalism and socialism; on societal axis you have authoritarian and libertarian politics, and on change axis you would have liberal and conservative politics.
There is some crosstalk between the axes, but the interactions between different axes are by no means clear-cut. For example, socialist views on economy require a degree of authoritarian beliefs.
On the other hand, the more extreme economical or societal political views one holds, the more conservative one is likely to be on a personal level: Stronger opinions are less likely to change.
So, I wouldn't necessarily relate conservatism and liberalism to any real politics since they are related to change, and typically conservatives are referred to as those who wouldn't like to change things from how they are; in different countries, these terms would have very different meanings. If you go and look at a conservative politician in let's say US, France, Finland and China, all these would likely be positioned somewhat differently on the economical and societal axes.
Instead, the conservative/liberal dichotomy should be used to describe personal attitude towards change and new ideals.