A social conservative is someone who supports right-wing politics on social issues. Examples of such issues are abortion, homosexual marriage, religion, capital punishment, euthanasia and similar issues. They may or may not be conservative on other issues, such as taxes.
In the United States social conservatives tend to be in the Republican Party and are usually also Christian Conservatives. There are also Americans who are social conservatives for other reasons than religion.
Some people, such as Mary Wollstonecraft, George Orwell, and Stephen Leacock, have supported left-wing politics on many issues. However, they were socially conservative on issues like abortion, for Wollstonecraft and Orwell, or feminism, for Leacock.