Brisket is cut from the breast section just below the chuck (there are two per carcass), and consists of two distinct areas separated by a layer of fat. The point (also called the deckle) is the richly marbled, fatty section that sits on top of the flat, the bigger, leaner bottom section.
When you're talking Texas brisket, you're talking about a full, packer cut brisket (point and flat intact) that weighs anywhere from 8 to 12-plus pounds. This is what pitmasters smoke at "low and slow" temperatures (225°F to 250°F) via indirect heat for 8 or more hours. If you're browsing the meat section of the average grocery store, the 2- to 6-ish-pound hunk of meat labeled "brisket" is most likely a trimmed flat (also called the first cut). This is the cut for slow cookers, braising, and other moist heat cooking; if you cook it for hours and hours like a Texas brisket, it will have the textural appeal of leather.