What is the terms applets and servlets mean?

This topic explains the differences between an applet and a servlet:

An applet:is a small application that extends the functionality of a Web browser.

A servlet:is a small piece of code that extends the functionality of a server.

Technically, a servlet is an object, written in Java, that is equipped to receive a request and to construct and send back a response. Because servlets are written in Java, they inherit all the language's power and strengths. One of these strengths is speed, as a great deal of effort has been put into making Java perform well as a server language. Equally important, Java is also a cross-platform technology, so it is possible to develop a servlet under Linux, deploy it on NT, and move to Solaris when the site grows, all without needing to change or recompile anything.

The servlet architecture is designed to eliminate the need to reload anything every time a request is made by the browser.