If you mean in sentences like the following, where "because" and "cause" are used as a conjunction, then there is no difference. I didn't do it because I didn't want to. I didn't do it cause I didn't want to. "cause" is an informal form of "because". "cause" can also be a noun or a verb.

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A quick note on the two answers above: It's less common in the UK to shorten 'because' to 'cause' or 'coz', unless in an extremely relaxed social situation ie a text or instant message to a close friend.

It depends in what context. If cause is used for because, then it is more of an casual way to say it. As you would see in musical lyrics "cos" or "cause" But for the actual definition of cause , the dictionary would give you the term "reason" Example: The "cause" of this accident was because of the speeding truck Casual term: I don't think I'll be going to the mall today cause of my back pain. I don't think I'll be going to the mall today because of my back pain.