What's an 'Edison'?

On Tuesday, March 10, 2015, Sarah Pritchard <sarahloupritchard@gmail.com> wrote:
Hi friends,
I'm helping with Abby Crain's performance in the ballroom this weekend and we're looking for some extra extension cords.

Please email me if you have any of the following that you would be willing to lend on Friday and Saturday nights. Comp tickets to the show for anyone who loans equipment!

We need:
1 12x 15' Edison
1 6x 50' Edison
1 4x 25' Edison

Thanks so much!
Sarah