Avalon is the name of a bus which was developed from Altera for using it in FPGA systems. The Avalon bus is used for connecting SOPC (system on a programmable chip) components together (e.g. the soft processor Nios, SDRAM controller, etc.). The detailed specification is available from Altera: **broken link removed**
AVALON is the terminology used by altera for the interfacing bus used in NIOS systems. for more information you can visit ALTERA website and search for pdf having full details regarding avalon switch matrix.