You asked, so here are a couple photos to show you just what a virtual crate is.
Here's the Dogmobile. Kate and Don bought it in September 1999 for the express purpose of trucking around the Monster Dogs, their four retired racing greyhounds. Naturally, for safety's sake, they planned for the dogs to travel in crates. Unfortunately, the Dogmobile had room for only three crates. The space left over, inevitably, became the virtual crate.
That's the virtual crate there on the left, next to the extra large crate required by alpha dog Chance. Usually, Rufus rides in the virtual crate, because he is the only one of the four who can be trusted not to jump out the minute the hatch is opened.
And that's what a virtual crate is.