What is IUPAC?
The chemistry world government.
IUPAC stands for the International Union of Pure and Applied Chemistry.
They set the rules for standardised naming, terminology, methods and data about chemicals. Some things can be measured wrongly or have a grey area - it is IUPAC who decide what the standard measurement should be, so all calculations use the same numbers.
They also publish articles and journals, organise conferences and have some public interactions.
It is easy to simply think of IUPAC as the chemistry world government.