Renderscript is a component of the Android operating system for mobile devices. It is an API for intensive computation using heterogeneous computing. It allows developers to increase the performance of their applications at the cost of writing a greater amount of more complex code. It provides the developer three primary tools: A general purpose compute API across different system computing hardware, a compute API similar to CUDA, OpenCL or GLSL, and a familiar language with C99. It can also be used for 3D graphics. Android 4.2 added new capabilities to script intrinsics, such as Blend and Blur; as well as ScriptGroups which allow you to chain together related Renderscript scripts and execute them with one call.
Most recently, Google added Filterscript, which is a subset of Renderscript that allows developers to write their image processing operations in Filterscript using the standard Renderscript runtime API, but within stricter constraints that ensure wider compatibility and improved optimization across CPUs, GPUs, and DSPs. Filterscript is a less precise in terms of numeric datatype precision, and more cross device compatible subset of Renderscript – and should not be mistaken for a Renderscript replacement technology. 
Simplify development as much as possible. Where possible steps are automated to avoid glue code
It's these trade-offs that separate Renderscript from the existing approaches on the device, such as Dalvik or the Android Native Development Kit. They should be thought of as different tools intended to solve different problems.