Something pocket-sized is small enough to slip into a pocket, or small enough to carry without fuss. Books, radios, maps, and now phones have all been called pocket-sized when the maker wants you to feel they will travel with you. You can also write pocket-size, with no d; both are used. People stretch it a little: a pocket-sized version of a big machine is just a much smaller copy, even if it would not actually sit in your pocket. The tone is usually practical, sometimes a bit proud of how small a thing is. It is not a rude word, though it can sound slightly dismissive if you call a serious plan pocket-sized, as if it were a toy.