Adafruit OLED 7 Pin Display - Abbreviations
DC selects between Data and Commands.
CS is the Chip Select
SDA is the Serial DAta.
SCL is the Serial CLock.

These four together form what the documentation calls the &quot;4-wire serial interface&quot;. It's not quite like SPI, owing to the presence of the DC pin (which is why it doesn't use SPI terminology), but close enough that SPI can be used to communicate with it.
In SPI the pin that sends data from the Arduino to the slave is known as the MOSI - Master Out Slave In.  Some microcontrollers also call this SDO - Serial Data Out, where it's &quot;out from the master's perspective&quot;.