Packages are new to the Mac OS and are designed to make it easier to for developers to keep all of the files related to a program in one place where regular folks won't have to worry with them. Basically they are folders that act like a file. When you double click on a package, it acts like an alias to open the application that is actually contained in the package.
It's not something the average user needs to worry about, at least not yet. Right now, very few developers are using them, at least in public. We should start to see more of them, especially in shareware installations (they have much shorter turnaround times and usually are quicker to embrace new technology than the big guys)
[This message has been edited by Don Foy (edited 11-02-1999).]