Swiss cheese is a general term, mainly used in North America, for cheeses made in the Emmental style: a pale yellow, semi-hard cow's-milk cheese with round holes ("eyes") formed by carbon dioxide released during fermentation. It's worth distinguishing from cheese made in Switzerland generally: most actual Swiss cheeses, such as Gruyère, Appenzeller, and Sbrinz, don't have holes at all; "Swiss cheese" as sold in North America usually means Emmental or an Emmental-style cheese.
Alpine cheesemaking in Switzerland dates back many centuries, shaped by the abundance of milk from cattle grazing summer alpine pastures. The cheese is central to dishes like fondue (cheese melted with white wine, garlic, and kirsch, served with bread) and raclette (cheese melted and scraped onto plates with potatoes and cured meats).
Its flavor is nutty, mildly tangy, and slightly sweet. It pairs well with cured meats, apples, pears, grapes, and herbs like thyme, and is a common addition to sandwiches, quiches, and tarts.