Difference between selenium webdriver and Appium in terms of client applications supported

Selenium web driver says they support mobile web applications only. Appium says they support native mobile apps and also mobile apps. As I understand
Appium uses Selenium-WebDriver for browser automation
Appium uses uiautomator (API level >= 17) and Selendroid ( API level < 17)
IOS Via UI Automation
Webdriver model referred in documentation of Appium is different web driver in selenium.

Can some one help me clarify my understanding?