SPI - Serial Peripheral Interface
SPI0 pins are GPIO 7, 8, 9, 10, 11
SPI1 pins are GPIO 16, 17, 18, 19, 20, 21
Known as the four-wire serial bus, SPI lets you attach multiple compatible devices to a single set of pins by assigning them different chip-select pins.
To talk to an SPI device, you assert its corresponding chip-select pin.
By default the Pi allows you to use SPI0 with chip select pins on CE0 on GPIO 8 and CE1 on GPIO 7.
You can enable SPI1 with a dtoverlay configured in "/boot/config.txt", for example:
For full details of the SPI dtoverlays (and others) see the Raspberry Pi dtoverlay README