Strain due to a departure in bond
angle from '
normal' values. The term is often used in the context of non-aromatic cyclic compounds in which the internal angles differ from the regular tetrahedral
angle of

; in this sense
angle strain is also known as Baeyer strain.
Source:
PAC, 1996, 68, 2193
(Basic terminology of stereochemistry (IUPAC Recommendations 1996))
on page 2198