What is the difference between Page Object Model and Page Factory in Selenium?

public class LoginPage {
    private WebDriver driver;

    // Locators defined as By objects
    private By emailInput    = By.id("email");
    private By passwordInput = By.id("password");
    private By loginBtn      = By.cssSelector("[data-testid='login-btn']");

    public LoginPage(WebDriver driver) {
        this.driver = driver;
    }

    public void login(String email, String password) {
        // Element found EVERY TIME method is called
        driver.findElement(emailInput).sendKeys(email);
        driver.findElement(passwordInput).sendKeys(password);
        driver.findElement(loginBtn).click();
    }
}

import org.openqa.selenium.support.FindBy;
import org.openqa.selenium.support.PageFactory;

public class LoginPage {
    private WebDriver driver;

    // @FindBy annotations replace By.id(), By.css() etc.
    @FindBy(id = "email")
    private WebElement emailInput;

    @FindBy(id = "password")
    private WebElement passwordInput;

    @FindBy(css = "[data-testid='login-btn']")
    private WebElement loginBtn;

    @FindBy(className = "error-msg")
    private WebElement errorMessage;

    // Multiple locators — tries each until one works
    @FindAll({
        @FindBy(id = "submit"),
        @FindBy(css = "button[type='submit']")
    })
    private WebElement submitBtn;

    // List of elements
    @FindBy(css = ".product-card")
    private List<WebElement> productCards;

    public LoginPage(WebDriver driver) {
        this.driver = driver;
        // This initializes all @FindBy elements (lazy — located on first use)
        PageFactory.initElements(driver, this);
    }

    public void login(String email, String password) {
        emailInput.sendKeys(email);      // clean — no driver.findElement()
        passwordInput.sendKeys(password);
        loginBtn.click();
    }

    public String getErrorText() {
        return errorMessage.getText();
    }
}

@FindBy(id = "email")                          // By.id
@FindBy(name = "username")                      // By.name
@FindBy(className = "error-msg")               // By.className
@FindBy(tagName = "h1")                        // By.tagName
@FindBy(linkText = "Forgot Password")          // By.linkText
@FindBy(partialLinkText = "Forgot")            // By.partialLinkText
@FindBy(css = ".btn.btn-primary")              // By.cssSelector (most used)
@FindBy(xpath = "//button[@type='submit']")    // By.xpath

// Page Factory can cause StaleElementReferenceException
// if DOM changes AFTER initElements() but BEFORE the element is used

// Solution: re-initialize on stale
public WebElement getElement(WebElement element) {
    try {
        return element;
    } catch (StaleElementReferenceException e) {
        PageFactory.initElements(driver, this);  // reinitialize
        return element;
    }
}