What are different forms of selenium?

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.firefox.FirefoxDriver;

public class SeleniumForms {
    public static void main(String[] args) {

        // Selenium WebDriver - Chrome
        WebDriver chromeDriver = new ChromeDriver();
        chromeDriver.get("https://www.google.com");
        System.out.println("Chrome Title: " + chromeDriver.getTitle());
        chromeDriver.quit();

        // Selenium WebDriver - Firefox
        WebDriver firefoxDriver = new FirefoxDriver();
        firefoxDriver.get("https://www.google.com");
        System.out.println("Firefox Title: " + firefoxDriver.getTitle());
        firefoxDriver.quit();

        // Selenium Grid - Remote WebDriver example
        // DesiredCapabilities caps = new DesiredCapabilities();
        // caps.setBrowserName("chrome");
        // WebDriver remoteDriver = new RemoteWebDriver(
        //     new URL("http://hub:4444/wd/hub"), caps);
    }
}