1. Literally, indicative of a sparing application. Frugal.
2. In the U.S., commonly used by many members of the Republican Party to contrast themselves with liberal
politicians, commonly of the Democratic Party.
3. Originally used by Republican Party (U.S.) members to mean conservative application of laws, or minimal government.
4. In modern times, used to indicate existing or past values as opposed to new values. In this sense, "conservative" refers to personal behavior rather than the use of laws. A synonym for this definition would be "unchanging."
When using the word, it is important to note whether it is used to refer to a political theory/system or personal values/behavior.
In the case of number 3 above, both the Republican and Democratic parties hold conservative _political_ values (in that they want minimal government regulation), but about different subjects. For example, the Democratic Party typically believes in conservative (minimal) use of laws regarding drugs, sexual practices, and film/TV. The Republican Party does not follow conservative political theory in those matters, but does for issues of taxation, guns, and employment practices.
However, even though both parties hold conservative political values in some cases, neither maintains a consistant philosophy based on conservative application of government regulation. Both the Republican and Democratic parties in the U.S. use the word to refer to enforcing conservative _personal_values_ (such as those influenced by religious background or otherwise, see number 4 above), but with differing opinions as to whether or not it is a good thing.
The original political use for the word conservative, as in number 3 above, is more similar to the political adjective/noun libertarian
in use today, which describes a philosophy of minimal government,