Collar Break. A portion of the inside wall of a collar which has cracked and broken away. A piece struck within a broken collar will exhibit a projection – a small flange – on the edge of the struck piece corresponding to the area broken away from the collar. Collectors call this anomaly a collar cud. If the collar was reeded, the reeding breaks away, and, of course, there is no reeding on the edge of the struck piece at that point. The collar cud will project beyond the normal diameter and reeding of the coin.

Reference:

NM19 {1991} Margolis, p 175-180.