In scientific research, the null hypothesis is the claim that no relationship exists between two sets of data or variables being analyzed. Wikipedia

A hypothesis that there is no relationship between two measured phenomena Wikipedia Disambiguation

Statistical concept Wikidata

A hypothesis set up to be nullified or refuted in order to support an alternative hypothesis. When used, the null hypothesis is presumed true until statistical evidence in the form of a hypothesis test indicates otherwise. Therefore, the null and the alternative hypothesis must be mutually exclusive and exhaustive. Wiktionary

Hypothesis. Wiktionary (translation)