The OSL Texture node is used to create scripts using the Open Shading Language in order to define arbitrary texture types and create customized OctaneRender® materials and shaders. It is a "catch-all" node that can be used to load any OSL script that is compatible with Octane. For a list of OSL features supported by Octane, see this link. 



Other OSL nodes are sorted into specific categories by either typical use or by author. That said, any OSL shader will work with any script or script type. The sorted OSL nodes are merely a convenience, not a restriction.