prior probability

https://doi.org/10.1351/goldbook.11496

The conditional probability that is assigned to a quantity before relevant evidence is taken into account, for example, the prior probability of an active compound would be the fraction of the compounds in the dataset that are active.

Note: The prior and posterior probabilities are linked by the (normalized) likelihood function (Bayes theorem).

Source:
PAC, 2016, 88, 239. 'Glossary of terms used in computational drug design, part II (IUPAC Recommendations 2015)' on page 253 (https://doi.org/10.1515/pac-2012-1204)