What is the significance of System.setProperty() while working with Selenium

Question

In selenium, why do we add System.setProperty("webdriver.chrome.driver", "E://chromedriver.exe"); within static{} block ?

public class Demo{
static{
System.setProperty("webdriver.chrome.driver", "E://chromedriver.exe");
}
  public static void main(String[] args) {
        WebDriver driver = new ChromeDriver();              
        driver.get("http://www.google.com");

    }
}