It doesnt work in debian. So who knows...

  # apt-get install @lxde-desktop
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done
  E: Unable to locate package @lxde-desktop

No, I think it is a group shortcut. As in install all packages in the group lxde-desktop.

Do you mean task? As in a synonym for

  apt-get install task-lxde-desktop