What is MAVLink?

From the official MAVLink site:

MAVLink (Micro Air Vehicle Communication Protocol) is a very lightweight, header-only message marshalling library for micro air vehicles.

See official MAVLink site for more info.

How is MAVLink definied?

MAVLink messages are definied in an XML files. You can look up the messages in the official MAVLink repository.

What is JaveLink?

JaveLink is a code generator that takes message definition xml files and generates java code.