“Sea” scallops are the big-sized scallops, as opposed to “bay” scallops. They are usually pretty expensive.
Sea scallops can be purchased “wet” or “dry”, and dry is preferred because they don’t splatter (and shrink) while cooking, and also because they don’t have chemical additives. They are not labeled wet or dry on the package, although if you read the ingredients you might figure it out. But if you buy them at a seafood counter, the counter-person usually won’t be able to tell you much about the wet or dry thing. If you pay a lot, you probably are getting dry scallops, but you can’t be sure.
In 2012 I came upon a Cooks Illustrated discussion of how to tell whether you have purchased wet or dry scallops. Take one scallop and put it on a paper towel in the microwave. Microwave on high for 15 seconds. If the paper towel has a lot of water on it, they are wet; if not, they are dry. (You can go ahead and use the zapped scallop in a recipe.)
If you have wet scallops, all is not lost. According to Cooks Illustrated: “soak them in a solution of 1 quart cold water, 1/4 cup lemon juice, and 2 tablespoons table salt for 30 minutes.”