When combined, 海峡两岸 (hǎixiá liǎng'àn) literally means “the two shores of the sea strait.” In 99.9% of modern usage, this specific strait is the Taiwan Strait (台湾海峡).
The term 海峡两岸 (hǎixiá liǎng'àn) is far more than a simple geographical descriptor; it's a cornerstone of political discourse surrounding Mainland China and Taiwan. Its primary function is to provide a framework for discussion that avoids taking a definitive stance on Taiwan's political status. By referring to “two shores,” it sidesteps the sensitive words “countries” (国家) or “nations.” This terminology is acceptable to and heavily used by the government in Beijing (PRC) and was historically favored by the Kuomintang (KMT) party in Taipei (ROC), as both sides subscribed (with different interpretations) to the idea of “One China.” A helpful Western comparison is the term “the Blue and the Gray” used to refer to the Union and the Confederacy during the American Civil War. This term described the two opposing sides of a single conflict within one nation, rather than two separate countries at war. Similarly, 海峡两岸 frames the situation as an internal, unresolved issue between two parts of a greater China. Using this term signals an understanding of the political sensitivities and is the standard for formal communication, journalism, and diplomacy in the region.
You will encounter this term constantly in news, political speeches, and academic papers, but almost never in casual, everyday conversation.