negotiation between nations
"The ambassador used careful diplomacy to resolve the border dispute between the two nations without going to war."
subtly skillful handling of a situation
"Her diplomacy allowed her to resolve the heated argument without anyone losing face."
wisdom in the management of public affairs
"The ambassador's reputation for diplomacy earned him praise for handling sensitive international disputes with remarkable grace and foresight."
The art and practice of conducting international relations by negotiating alliances, treaties, agreements etc., bilaterally or multilaterally, between states and sometimes international organizations, or even between polities with varying status, such as those of monarchs and their princely vassals.
"The ambassador's primary duty was to practice diplomacy by negotiating a new trade treaty directly between the two nations."
In plain English: Diplomacy is using polite talk and careful planning to solve problems between groups of people without fighting.
"She used her diplomacy to calm everyone down during the argument."
Usage: Avoid using "diplomacy" to describe personal social skills; the term specifically refers to statecraft and official negotiations. It is also distinct from "diplomat," which denotes the person performing these duties rather than the practice itself.
The word diplomacy entered English via the French term diplomatie, which was originally derived from diplomate. This root traces back to the Latin diploma, meaning a formal document such as a letter of recommendation or official authorization.