SPI - what is Data Ready?

Projects Networking, Protocols, and Devices
1

I'm using a sensor that communicates over SPI with an arduino. I found a library to interface with it that uses a Data Ready pin. When the pin goes high it triggers an interrupt that reads the data.

I'm wondering what a Data Ready pin is and how to use it.

I'm also wondering what's up with this phrasing of code

// Data Ready Flag
boolean validData = false;

// Call ADIS16448 Class
ADIS16448 IMU(7,2,4); //ChipSelect,DataReady,Reset Pin Assignments

void setup()
{
  Serial.begin(115200); // Initialize serial output via USB
  IMU.configSPI(); // Configure SPI communication
  
  delay(100); // Give the part time to start up
  IMU.regWrite(SMPL_PRD,0x1), // Set Decimation on IMU
  delay(20);
  
  // Read the control registers once to print to screen
  MSC = IMU.regRead(MSC_CTRL);
  SENS = IMU.regRead(SENS_AVG);
  SMPL = IMU.regRead(SMPL_PRD);
  
  attachInterrupt(0, setDRFlag, RISING); // Attach interrupt to pin 2. Trigger on the rising edge
  
}

I think it might have something to do with this but I don't know.

////////////////////////////////////////////////////////////////////////////
// Constructor with configurable CS, DR, and RST
////////////////////////////////////////////////////////////////////////////
// CS - Chip select pin
// DR - DR output pin for data ready
// RST - Hardware reset pin
////////////////////////////////////////////////////////////////////////////
ADIS16448::ADIS16448(int CS, int DR, int RST) {
  _CS = CS;
  _DR = DR;
  _RST = RST;

  SPI.begin(); // Initialize SPI bus
  configSPI(); // Configure SPI

//Set default pin states
  pinMode(_CS, OUTPUT); // Set CS pin to be an output
  pinMode(_DR, INPUT); // Set DR pin to be an input
  pinMode(_RST, OUTPUT); // Set RST pin to be an output
  digitalWrite(_CS, HIGH); // Initialize CS pin to be high
  digitalWrite(_RST, HIGH); // Initialize RST pin to be high
}