What is an Applets?
Applets: These are small java programs.
They can send from one to another computer over internet by using Applet Viewer which supports java.
Applets can run in a Web browser because it's a java program. It can be a fully functional Java application as it has entire Java API at its disposal.
Applets follow security rules provided by Web browser.
Applet security is also termed as sandbox security.