A card that seems to help no one.
When a brick falls the order doesn't change, so you can keep playing the way you decided on the flop. Example. A 2 falling on K-8-3 completes no draw. For the low in Razz and Stud 8, a brick is a 9 or higher, or a card that pairs you. From a three-card low, you catch a good card on 4th street 41% of the time and a brick 59%.