'Convention' is Latin for 'a coming together' — customs, treaties, and gatherings from one metaphor.
A way in which something is usually done; an agreement between states or parties; a large meeting or conference of people who share a common interest.
From Latin conventiō (a meeting, assembly, agreement), from convenīre (to come together, to agree, to fit), composed of con- (together) + venīre (to come), from PIE *gʷem- (to come, to step). The PIE root *gʷem- is one of the most productive in Indo-European: it gives Latin venīre (come), Greek bainō (I walk, step), Sanskrit gacchati (he goes), and distantly English come and become. The three main modern senses of convention all derive from different aspects of coming-together
The French Revolution's governing body was called the 'Convention nationale' (National Convention, 1792–1795), and in American history, the Constitutional Convention of 1787 framed the U.S. Constitution. Both were landmark uses of the word for an assembly that shaped a nation. The sense of 'convention' as 'an established custom or norm' arose from the idea that social rules are things