To help clarify the role of the Java interpreter, consider a hypothetical interpreter for a human language. Pretend you only speak French and your word processor only understands French. Let us also assume that someone has written you a letter in English.
In order to process the English letter your word processor would need an English-to-French translator, or interpreter. The job of this interpreter is to translate English words into French words and present you with a French letter that you can read. Any ideas as to where this analogy is headed?
French is equivalent to the native code of your computer while English is akin to generic Java bytecodes. The Java interpreter works very much like this human language interpreter because it takes Java bytecode and translates it into a form understood by different computing platforms.