A gob is a lump, blob, or chunk of something. A gob of pizza dough has to be flattened into a large circle before you can top it with sauce and cheese and bake it in the oven.
A gob can be a hunk of something slimy or yucky — you might avoid stepping on an unidentified gob on the sidewalk. You can also eat a gob of cookie dough or mold a gob of clay. Roald Dahl introduced the Everlasting Gobstopper in his novel "Charlie and the Chocolate Factory" as a form of candy that would last forever. A more old fashioned meaning of the word gob is "a sailor." While the origin of this kind of gob is a mystery, the "lump" meaning comes from gobbet, "fragment," rooted in the Old French gobet, "piece or mouthful."