What is a 966cm-1 trans fat band?

966 reciprocal centimeters (actually 960-990 or so) is the frequency associated with the C-H bending frequency of a trans double bond in IR spectroscopy. A material that shows an absorption band at this frequency is likely a trans alkene, such as a trans fatty acid. (Monosubstituted alkenes also have a band in this region, but they have an additional bending band around 900 cm-1 that trans alkenes do not.)