In the Old Testament the ephod has two meanings. In one group of passages it signifies a garment; in another, very probably an image. As a garment the ephod is referred to in the priestly ordinances as a part of the official dress of the high priest. It was to be made of threads “of blue and of purple, of scarlet, and fine twined linen” and embroidered in gold thread “with cunning work” (Exodus 28:4, 29:5, 39:2; Leviticus 8:7).
The ephod was held together by a girdle of similar workmanship sewed on to it. It had two shoulder pieces, which, as the name implies, crossed the shoulders, and were apparently fastened or sewed to the ephod in front. In dressing, the shoulder pieces were joined in the back to the two ends of the ephod. Nothing is said of the length of the garment. At the point where the shoulder pieces were joined together in the front “above the girdle,” two golden rings were sewed on, to which the breast-plate was attached.
The word “ephod” has an entirely different meaning in the second group of passages, all of which belong to the historical books. It is certain that the word cannot here mean a garment. This is evident in Judges 8:26–27, where it is recorded that Gideon took the golden earrings of the Midianites, weighing 1,700 shekels of gold, and made an “ephod thereof, and put it in his city, even in Ophrah,” where it was worshiped by all Israel. In Judges 17:5, Micah made an ephod and teraphim, or idol, for his sanctuary. The most natural inference from all these passages is that “ephod” here signifies an image that was set up in the sanctuary, especially since the word is cited with teraphim, which undoubtedly refers to an image (Hosea 3:4). The conclusion is that ephod, in these cases, referred to a portable idol. Some scholars have suggested that the connection between the idol and the garment is that the idol was originally clothed in a linen garment, and the term ephod gradually came to describe the idol as a whole.
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.