Unless you're a real beef enthusiast or a passionate pitmaster, you may not be familiar with a deckle of beef. Put simply, a deckle is a type of beef brisket.
If you've eaten or prepared brisket, it likely was what's called first-cut or the flat cut. The deckle is known as the second cut.
The deckle goes by several other names, including ribeye cap, point, cap of ribeye, the more scientific title Spinalis Dorsi, and the imagery-inducing moniker "butcher's butter."
Like its leaner counterpart, it can be smoked or grilled, but its higher fat content makes it a candidate for other preparations.
You may need to work a little harder to find deckle. Try asking the store’s meat department if they have any in the back, or visit your town's butcher shop.