Any
person who wants the
federal,
state, or
local government to not only
refuse to give more
personal freedom, but to add more
laws to
restrict the things
people are allowed to do in their
personal life, usually (but not always) in the name of
morality, especially
religious morality (the
Christian morality in the
USA).
Someone who wants more laws to change the behavior of their neighbors. Essentially, only the things they want to do should be legal.
Not necessarily the same as a conservative in other fields, such as economic issues, though there is quite the overlap. In fact, while economic conservatives usually want smaller government, many laws pushed by social conservatives require bigger government, as it must be more involved in people's personal lives.