虚包－Virtual package

 A virtual package is one which appears in the Provides control file field of another package. The effect is as if the package(s) which provide a particular virtual package name had been listed by name everywhere the virtual package name appears. (See also Virtual packages, Section 3.6)

If there are both concrete and virtual packages of the same name, then the dependency may be satisfied (or the conflict caused) by either the concrete package with the name in question or any other concrete package which provides the virtual package with the name in question. This is so that, for example, supposing we have

     Package: foo
     Depends: bar

and someone else releases an enhanced version of the bar package they can say:

     Package: bar-plus
     Provides: bar

and the bar-plus package will now also satisfy the dependency for the foo package.

所谓虚包，就是这个包的包名会出现在别的包的control文件的Provides域中。例子中foo依赖bar,而bar是个由bar-plus提供的虚包，这样foo就转而依赖bar-plus了。