As I understand it, rdepends lists packages which depend on the specified package.
Example:
$ apt-cache rdepends abiword
abiword
Reverse Depends:
abiword:i386
xubuntu-desktop
|python-carquinyol-0.96
pkpgcounter
lubuntu-desktop
junior-writing
gnome
|freemind-doc
abiword-plugin-mathview
abiword-plugin-grammar
abiword-dbg
In this output, what does | mean?
As per this question, it means 'or' in apt-cache depends, however that doesn't seem relevant here (package1 or package2 depending on abiword is impossible).