The written forms of definitions ought to meet certain requirements in order to be generally acceptable among lexicographers and terminographers. This article reviews the theoretical and specific guidelines for definitions laid down by some philosophers and terminology organizations. It assesses the extent to which guidelines have been adhered to in a corpus or terminological definitions, such as BS/ISO 2328: Data Processing and information technology Vocabulary. It points out the deviations of the definitional phrase patterns and proposes methods for expanding and reducing patterns for standardization purposes.