Smallest and weakest animal of a litter.
Note: A runt may be disadvantaged in competing with its siblings for resources and its mother’s attention.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 802 (https://doi.org/10.1515/pac-2015-1202)