The OSL projection node is a scriptable Node where you write OSL (Open Shader LanguageA shading language developed by Sony Pictures Imageworks. There are multiple render engines that utilize OSL as it is particularly suited for physically-based renderers.) scripts using the defined arbitrary Projection types. It works similar to an OSL texture node, but connects to a Projection input. To learn about the generic OSL standard, information is provided from the OSL Readme and PDF documentation.
Figure 1: The OSL Projection parameters