Whats the dram eq?

I was looking at one of my boxes of shotgun shells the other day and I seen that the dram eq. Was 3. I was wondering if anyone knew what that was and could explain it to me. Thank you.

Evidently has something to do with the measurement of grain contained in a shell - found 2 definitions:

Definition 1. a unit of apothecaries' weight equal to sixty grains or one eighth of an ounce.
Definition 2. a unit of avoirdupois weight equal to 27.344 grains or one sixteenth of an ounce.

Hope this helps !!