Glossary:SPI
SPI is a method of relatively high speed serial communication between ICs or subsystems in a device. It is used by SDCards and memory ICs more generally, as well as by displays and numerous other devices. It uses a clock line (SCLK) which simultaneously marches data in both directions using the two data lines MOSI (Master Out Slave In) and MISO (Master In Slave Out), making a minimum of 3 connections.