"四大发明" refers to the four great inventions of ancient China: 纸 (paper), 火药 (gunpowder), 印刷术 (printing), and 指南针 (the compass). These innovations significantly influenced not only Chinese society but also the world, facilitating communication, exploration, and warfare. 纸 allowed for the recording of information, while 印刷术 made books more accessible. 火药 transformed military technology, and the 指南针 improved navigation. Together, these inventions played a crucial role in the development of culture and technology throughout history.