It is a law. Jongin couldn't tell you what type of law as he isn't well versed in the field of physics (magical beings are more his forte) but this particular law is definitely the backbone of the world.

The universe tends towards chaos.

Chaos is the five letter word which continues to hang Kyungsoo around like a bad smell. Whatever he does he can't get rid of its' lingering scent. He decrees the word chaos should be crossed out in the english dictionary and replaced by the name 'Kim Jongin'.

It seems only fitting.

Jongin decrees the definition of universe should be 'Kyungsoo'.

Kyungsoo retorts Jongin's sacred law is wrong; he rather believes in chemical equilibriums.