וַיֹּאמֶר אֶל אֶבְיָתָר הַכֹּהֵן הַגִּישָׁה הָאֵפוֹד
The ephod was one of the garments worn by the Kohein Gadol. It looked something like an apron. The choshen (which contained the Urim V'tumim) rested on the ephod.
Below are some links to pictures of the ephod. Click on the thumbnails to go the page where the images are located.