Fundamentalism and the original, 'classic' stuff are two different kettles of fish.
The traditional way to start a post like this is to pull your Merriam-Websters dictionary off the shelf and copy out their definition, so here is what they say:
a often capitalized : a movement in 20th century Protestantism emphasizing the literally interpreted Bible as fundamental to Christian life and teaching
There's more to it of course, but that's a place to start. Authentic, historic Christianity (see this and this for what that is), however, is different from fundamentalism in a host of ways. Here are 10:
Historic Christianity (HC) - Longevity: two millennia
Fundamentalism (F) - Longevity: since the 1895 Niagara Conference
HC - A faith shared worldwide by believers for 20 centuries in diverse generations and cultures
F - A particular crisis between parties within North American Protestantism
HC - Has lived though and beyond hundreds of alleged "modernities"
F - A defensive response to particular challenges of nineteenth-century "modernity," especially Darwinism and rising secular humanism
HC - A catholic (i.e., universal) and orthodox (i.e., right belief) faith established through authoritative texts tested in many cultures
F - A truncated orthodoxy is cast in terms of the crisis of modernity, lacking in the whole fabric of historic, orthodox belief
HC - Confident through historical change based on historic experience
F - Often expecting the worst from the human future
HC - Recognition of metaphor and varieties of expression of inspired doctrine in scripture
F - Single legitimate interpretation of each text
HC - Texts viewed within historic contexts
F - Texts viewed apart from historic contexts
HC - Focuses on the meaning of scripture
F - Focuses on the historicity of scripture
HC - A work of the Spirit leading Christ's disciples "into all truth" (John 16.13 ) until they reached a consensus
F - A literal approach to scripture
(Adapted from Classic Christianity, Thomas Oden, pp. xxiv - xxv)
I have some friends who really dislike fundamentalists, but I don't feel that way. After all, as I've mentioned, I used to be a fundamentalist myself so I definitely sympathize. But it is a recent and rather constricted approach to trying to understand Jesus and the Bible. My point here is just that even though fundamentalism may get a lot of press, it's not the way Christianity has always been, and certainly not the way it was in the early church.
Gregory of Nyssa, one of those early Christians who helped unpack Jesus' teachings, once wrote, "Those who handle the text in too literal a manner have a veil cast over their eyes, whereas those who turn to contemplate the God of whom the Scriptures speak receive the revelation of divine glory which lies behind the letter of the text," (Gregory of Nyssa, Against Eunomius, 7.1).