Definition: A spiked head is a coin that has a straight die crack on the obverse, running from the edge of the coin into the portrait. This die crack is often seen on Proof coins, and can be anywhere on the rim extending into the portrait, or head. The example in the photo shows a Spiked Head proof Tennessee quarter, with the spike occurring at about 6:00. Another location for the die crack, often seen on Spiked Head coins, is the 1:00 position, although the crack can occur anywhere along the rim extending inward and touching the head.
Examples:
Although Proof coins are supposed to be of the highest quality, some of them in the State Quarters series are being found with spiked heads!