Definition
Affixation is concatenative morphological process, also described as process morphology, that involves the attachment of an affix to a given base. The type of affixation corresponds to the affix’s place of attachment and determines if it is an instance of prefixation, suffixation, infixation or circumfixation.
Examples

See affix, prefix, suffix, infix and circumfix for further examples of affixation across our languages of interest.
References