Transferability assumes invariance of properties, associated conceptually with an atom or a fragment present in a variety of molecules. The property, such as electronegativity, nucleophilicity, NMR chemical shift, etc. is held as retaining a similar value in all these occurrences.
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1173 (https://doi.org/10.1351/pac199466051077)