Moral absolutism is the meta-ethical view that some forms of human conduct are right or wrong (alternatively, good or evil) in any context. Even for the purpose of doing good, bad actions are always bad and cannot be justified.
The belief that the act of homicide is always immoral, even if it is committed to defend oneself, or perhaps several others, is a form of moral absolutism.
The majority of examples of absolute morality are found in religion, where an entire moral system is believed to come from the divine and is therefore true, certain and absolute to the highest possible degree.
There are, however, forms of absolutism that are accessible without religion. Kant, for example has some ethical views that tend towards absolutism without depending on religion.