Data source is an umbrella term for any piece of data attached to a Parameter (see the Parameter class in the C++ API) driving its value. It could be data that is animating a parameter (see the AnimationSourceItem object in the XSI Object Model or the AnimationSourceItem class in the C++ API) such as an Expression (see the Expression class in the C++ API), StaticSource (see the StaticSource class in the C++ API), Constraint (see the Constraint class in the C++ API) or an FCurve (see the FCurve class in the C++ API). It could be an Operator (see the Operator class in the C++ API). It could be a Shader (see the Shader class in the C++ API) or an ImageClip (see the ImageClip2 class in the C++ API) used on a texture projection or in the FxTree.
SOFTIMAGE|XSI v6.01