Definition - What does Additionality mean?
Additionality is a term used to describe what a certain technological activity or intervention has accomplished. Some call additionality a notional measurement in that it's a comparative measure (not inherently quantifiable) that helps clarify the effectiveness and capability of a particular technology or advancement.
Additionality helps to promote clarity in talking about what new technologies do and how they operate within various industries and areas of use.
Techopedia explains Additionality
To apply this to IT, think about some new technology, such as a data manipulation tool that produces a certain set of field results in a database in a certain sequence and number. To use the principle of additionality, developers or engineers would be looking at whether that data would be ordered that way without the use of this particular tool, or whether it would be in some other state. Clarifying with additionality would then allow the software product maker to claim that the program does certain things to data.