## borderline mechanism

https://doi.org/10.1351/goldbook.B00711
A mechanism intermediate between two extremes, for example a nucleophilic substitution intermediate between $$\text{S}_{\text{N}}1$$ and $$\text{S}_{\text{N}}2$$, or intermediate between @[email protected] and $$\text{S}_{\text{N}}2$$.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1090 [Terms] [Paper]