The Nine-Dash Line — refers to the undefined, vaguely located, demarcation line used initially by the Republic of China (1912–1949) and subsequently the governments of the Republic of China (ROC, which governs Taiwan) and the People’s Republic of China (PRC), for their claims of the major part of the South China Sea.
Despite having made the vague claim public in 1947, China has not (as of 2018) filed a formal and specifically defined claim to the area within the dashes.
China added a tenth-dash line to the east of Taiwan island in 2013 as a part of its official sovereignty claim to the disputed territories in the South China Sea.
On 12 July 2016, an arbitral tribunal constituted under Annex VII to the 1982 United Nations Convention on the Law of the Sea ruled that China has no legal basis to claim “historic rights” within its nine-dash line in a case brought by the Philippines. The tribunal judged that there was no evidence that China had historically exercised exclusive control over the waters or resources within the Nine-Dash Line. The ruling was rejected by both the PRC and ROC governments.