Marginally machine-readable mark

An intentional mark in a contest selection position of a paper ballot that does not meet the requirements for a reliably detectable selection, and therefore requires human adjudication. A marginal mark may be determined to indicate a selection, depending on state law.

Source: Election Terminology Glossary - Draft, National Institute of Standards and Technology (NIST), https://pages.nist.gov/ElectionGlossary/