A computer language or programming language is an artificial language designed to communicate instructions to a computer. The very first applications were written in a language that computers could directly execute, often called machine code.  However, machine code proved too difficult for a programmer to write anything but the simplest of applications.  Computer languages were developed by programmers for programmers to enable them to create more complex applications. These same programmers, also created special purpose applications that would convert or translate the application written in a computer language into machine code so that the computer could execute the application.
Computer source code is the name for one or more files or documents written in a computer language that makes up one or more applications.
Many computer languages are suitable for many different types of applications (e.g. C++ is used for many types of applications) and others are more specialized for specific kinds of applications (e.g. Javascript is mostly used for web pages). New computer languages are constantly being created and old ones enhanced -- all to make it easier to create more complex, more correct (less buggy), more secure and faster applications.
For more general and specific information about computer languages:

• Official Java Site
• C++ Resource Page
• An introduction to HTML from Mozilla (the Firefox people)