What is "graveyard zerging" or "death zerging"?

In a blog post by Blizzard they mention some practice called "graveyard zerging", for instance:

Our goal is the next time a player is graveyard zerging a boss, it should occur to them that "this is probably not an efficient way to go about things".

In another, later post they mentioned "death zerging", which I assume means the same thing.

What is "graveyard zerging", and how is it done?

From the context it seems that "boss" was used incorrectly. Just above in the same paragraph:

“graveyard zerging” tough enemies

It appears he meant graveyard zergling elites or uniques, which you can simply throw yourself at and then resurrect at the nearest checkpoint (or banner teleport to any nearby alive or recently dead player) and repeat the process.

He could have also meant his other example in the same line:

chain rezzing allies on a boss

There is no way to combine the two, you can not return to a boss by returning to the checkpoint.

This is the act of jumping in to do as much DPS to a boss as you can and dying but having a person available to revive you.. You do not care about your own safety just as long as that reviving person is still around.

"Graveyard zerging" is a term.

An example is when a full party encounters an elite pack, and all of them dies, a party member won't spawn so the others can corpse-banner (teleport to the dead member using the banner) to get back into the action. Basically it is just overwhelming an elite pack.

For solo play, you get to lure an elite pack to the nearest checkpoint/waypoint for you to get back into the action when you die.