A package name is supposed to be unique for your application / enterprise, so there is no conflict between your classes and those of somebody else. An example is the class (or interface) Element, that can be found in a dozen of different libraries, and Java alone has 5 of them! But they live in different packages, so as long as they are not used in the same class, there is no conflict. Otherwise, the compiler complains that there is an ambiguity on the class and one must use a fully qualified name, at least for one of the classes. Another example is java.awt.List (a graphical component) used along java.util.List (a collection). These names prefixed with package are the fully qualified name.

Now, how these package names are determined? A strong tradition, encouraged by Sun, is to use for the start of the package the URL of the company releasing the library, inverted. So, for Apache, it will be org.apache. For Oracle, it can be com.oracle. And so on. Behind, you have the folder sub-division to keep things neatly organized.
For example, Apache has org.apache.commons.lang, org.apache.commons.logging, etc. Then org.apache.commons.lang.stringutils, and so on.

Note that you must put the code in the folder structure you define thusly: if you have code in the com.example.util package, it must also be in the com/example/util folder, at the root of your source folder.

In the Processing world, things are often less formal, perhaps because lack of knowledge of what packages are (or are supposed to be), or because Processing "led the way" by using only the processing package, probably in the sake of simplicity.
So we have processing.opengl, ddf.minim.effects, guicomponents, controlP5 (breaking the implicit rule of using all lower case for package names), toxi.physics.behaviors and so on.
Another reason for these URL-less packages might be that they are often made by amateurs, not necessarily having an official Web site of their own. It can seem odd to have com.ispname.codername as package... (but why not). Some use the name of their code host, like com.github.somebody.someproject, but when they change to another, the reference can become obsolete...

Wow, I was verbose. I hope that helps.

that does indeed give me plenty to work with.. thanks.

In Processing 2.0a4 in Android Mode you'll find in the AndroidManifest.xml a line package="". There you can simply write your web address and the name of your app in it, for example package="com.myname.myapp". This will create a package/folder structure in your exported Android Projekt.

Well that's good to know in future. I ended up renaming all the sub-folders manually until it worked. The app is up on Google Play now.