What is indirect rendering and what sort of implications does it have on graphics performance?
Also, is it a Linux-specific term or can it be used in the context of other operating systems?
Indirect rendering is when a remote application is rendered on the local computer. It transports the graphics data over the X11 protocol. How it performs depends both on the network connection to transport the data and how good your local gfx card is.
It's applicable on any system with a gfx card and an running X-Server (windows or linux)
Indirect rendering as opposed to Direct rendering means your using some sort of software rendering instead of using your graphics card GPU. The results are poor 3D rendering.
Indirect rendering means no hardware graphics acceleration.