This rhetorical device might have a complicated-sounding name, but it is anything but. Every time you use a part of a sentence or grammatical structure to refer or represent the whole, you are using synecdoche. The same goes for things, people or events. So when people refer to America as a country, they could mean both the US and the two continents. But experience teaches us that they are probably referring to the nation. It is just easier to say one word than the whole structure, The United States of America. It is easy to confuse this device with a metonymy. But remember, metonymy addresses something with a term that is similar, while synecdoche uses a part of something to refer to the whole thing. Like boots to soldiers or wheels for cars.