What Does Fundamentalism Mean In Religious Terms?

A religious fundamentalist is someone who feels very passionately about their religion and who feels usually that all other people should share their views and their religion.  Often those people who do not are viewed as some kind of enemy or infidel.
Religious fundamentalists are not necessarily Christian, they can be found in all types of religion, although some such as Buddhism, try to actively discourage fundamentalist beliefs.  Some Muslims are fundamentalists as can some Sikhs, Jews or various other faiths.  They are often regarded as being at the more extreme end of religious belief.
Fundamentalism is often viewed by suspicion by the state because those holding power can feel slightly threatened by a religious group who claim that they have all the answers.  It is for this reason that fundamentalism is often mentioned on the news when regarding the political state of a nation.